When displaying a project's pipelines
(Projects::PipelinesController#index) we now exclude the coverage data.
This data was not used by the frontend, yet getting it would require one
SQL query per pipeline. These queries in turn could be quite expensive
on GitLab.com.

When displaying the pipelines of a project we now preload the following
data:

1. Authors of the commits that belong to these pipelines
2. The number of warnings per pipeline, which is used by
   Ci::Pipeline#has_warnings?

== Commit Authors

Previously this data was queried for every Commit separately, leading to
20 SQL queries being executed in the worst case. With an average of 3 to
5 milliseconds per SQL query this could result in 100 milliseconds being
spent in _just_ getting Commit authors.

To preload this data Commit#author now uses BatchLoader (through
Commit#lazy_author), and a separate module
Gitlab::Ci::Pipeline::Preloader is used to ensure all authors are loaded
before they are used.

== Number of warnings

This changes Ci::Pipeline#has_warnings? so it supports preloading of the
number of warnings per pipeline. This removes the need for executing a
COUNT(*) query for every pipeline just to see if it has any warnings or
not.

When displaying the project pipelines dashboard we display a few tabs
for different pipeline states. For every such tab we count the number of
pipelines that belong to it. For large projects such as GitLab CE this
means having to count over 80 000 rows, which can easily take between 70
and 100 milliseconds per query.

To improve this we apply a technique we already use for search results:
we limit the number of rows to count. The current limit is 1000, which
means that if more than 1000 rows are present for a state we will show
"1000+" instead of the exact number. The SQL queries used for this
perform much better than a regular COUNT, even when a project has a lot
of pipelines.

Prior to these changes we would end up running a query like this:

    SELECT COUNT(*)
    FROM ci_pipelines
    WHERE project_id = 13083
    AND status IN ('success', 'failed', 'canceled')

This would produce a plan along the lines of the following:

    Aggregate  (cost=3147.55..3147.56 rows=1 width=8) (actual time=501.413..501.413 rows=1 loops=1)
      Buffers: shared hit=17116 read=861 dirtied=2
      ->  Index Only Scan using index_ci_pipelines_on_project_id_and_ref_and_status_and_id on ci_pipelines  (cost=0.56..2984.14 rows=65364 width=0) (actual time=0.095..490.263 rows=80388 loops=1)
            Index Cond: (project_id = 13083)
            Filter: ((status)::text = ANY ('{success,failed,canceled}'::text[]))
            Rows Removed by Filter: 2894
            Heap Fetches: 353
            Buffers: shared hit=17116 read=861 dirtied=2
    Planning time: 1.409 ms
    Execution time: 501.519 ms

Using the LIMIT count technique we instead run the following query:

    SELECT COUNT(*)
    FROM (
        SELECT 1
        FROM ci_pipelines
        WHERE project_id = 13083
        AND status IN ('success', 'failed', 'canceled')
        LIMIT 1001
    ) for_count

This query produces the following plan:

    Aggregate  (cost=58.77..58.78 rows=1 width=8) (actual time=1.726..1.727 rows=1 loops=1)
      Buffers: shared hit=169 read=15
      ->  Limit  (cost=0.56..46.25 rows=1001 width=4) (actual time=0.164..1.570 rows=1001 loops=1)
            Buffers: shared hit=169 read=15
            ->  Index Only Scan using index_ci_pipelines_on_project_id_and_ref_and_status_and_id on ci_pipelines  (cost=0.56..2984.14 rows=65364 width=4) (actual time=0.162..1.426 rows=1001 loops=1)
                  Index Cond: (project_id = 13083)
                  Filter: ((status)::text = ANY ('{success,failed,canceled}'::text[]))
                  Rows Removed by Filter: 9
                  Heap Fetches: 10
                  Buffers: shared hit=169 read=15
    Planning time: 1.832 ms
    Execution time: 1.821 ms

While this query still uses a Filter for the "status" field the number
of rows that it may end up filtering (at most 1001) is small enough that
an additional index does not appear to be necessary at this time.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/43132#note_68659234
for more information.

Resolve "Opening Project with invite but without accepting leads to 404 error page"

Closes #42531

See merge request gitlab-org/gitlab-ce!17634

CE: Add jobs to verify that migrating from CE to EE works

See merge request gitlab-org/gitlab-ce!18909

Workhorse to send raw diff and patch for commits

Closes gitaly#1196

See merge request gitlab-org/gitlab-ce!18974

Remove unneccessary imports

See merge request gitlab-org/gitlab-ce!18993

Add dot to separate system notes content

Closes #45676

See merge request gitlab-org/gitlab-ce!18864

Delete remote uploads

Closes #45425

See merge request gitlab-org/gitlab-ce!18698

API support + Improved policies for group runners

Closes #45894 and #38979

See merge request gitlab-org/gitlab-ce!18851

Fix contributors graph width

Closes #22647

See merge request gitlab-org/gitlab-ce!18639

Fix Error 500 viewing admin page due to statement timeouts

Closes #46255

See merge request gitlab-org/gitlab-ce!18982

fixed copy to cliboard button in embedded snippets

Closes #46303

See merge request gitlab-org/gitlab-ce!18923

Adjust board lists header text color

Closes #36983

See merge request gitlab-org/gitlab-ce!18955

Uses PostgreSQL tuple estimates to provide a much faster yet approximate
count. See https://wiki.postgresql.org/wiki/Slow_Counting for more details.
We only use this fast method if the table has been analyzed or vacuumed
within the last hour.

Closes #46255

Remove table-section from div holding cluster error messages

See merge request gitlab-org/gitlab-ce!18971

edit GitLab license info in regards to CC licensing

See merge request gitlab-org/gitlab-ce!18981

Never drop the database when granting privileges

Move discussion and notes actions to the right

Closes #33645

See merge request gitlab-org/gitlab-ce!18476

Fix GitLab Performance Monitoring content types for Doorkeeper

Closes #46412

See merge request gitlab-org/gitlab-ce!18984

Project Sidebar: Split CI/CD into CI/CD and Operations

Closes #43673

See merge request gitlab-org/gitlab-ce!18941

Move Gitlab::Git::Repository#add_branch to mandatory

Closes gitaly#540

See merge request gitlab-org/gitlab-ce!18939

Certain controllers (e.g. Doorkeeper::TokensController) don't expose the
method "request_format". This commit changes
Gitlab::Metrics::WebTransaction so we don't rely on this method, instead
using the underlying code this method uses.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/46412

Remove docker pull prefix from registry clipboard feature

Closes #46314 and #45968

See merge request gitlab-org/gitlab-ce!18933

Prior to this change, this was done through unicorn. In theory this
could time out. Workhorse has been sending these raw patches and diffs
for a long time and is stable in doing so.

Added bonus is the fact that `Commit#to_patch` can be removed.

`Commit#to_diff` too, which closes
https://gitlab.com/gitlab-org/gitaly/issues/324

Closes https://gitlab.com/gitlab-org/gitaly/issues/1196