Add QUERY_RECORDER_DEBUG environment variable to improve performance debugging

See merge request gitlab-org/gitlab-ce!15499

Add support of Mermaid

Closes #3711

See merge request gitlab-org/gitlab-ce!15107

Add FetchSourceBranch Gitaly call

Closes gitaly#758

See merge request gitlab-org/gitlab-ce!15498

[ci skip]

Update composite pipelines index to include "id"

See merge request gitlab-org/gitlab-ce!15519

default fill color for SVGs

See merge request gitlab-org/gitlab-ce!15476

ignore hashed repos (for now) when using `rake gitlab:cleanup:repos`

Closes #40291

See merge request gitlab-org/gitlab-ce!15520

Set the default gitlab-shell timeout to 3 hours

Closes #39977

See merge request gitlab-org/gitlab-ce!15292

Use Redis cache for branch existence checks

Closes #40349

See merge request gitlab-org/gitlab-ce!15513

Update CONTRIBUTING.md: Link definition of done to criteria

See merge request gitlab-org/gitlab-ce!15500

FileUploader should use Hashed Storage only when project is migrated

See merge request gitlab-org/gitlab-ce!15526

Simplify Feature Proposal template

See merge request gitlab-org/gitlab-ce!15297

Use arrays in Ci::Pipeline#latest_builds_with_artifacts

See merge request gitlab-org/gitlab-ce!15525

Use `make install` for Gitaly setups in non-test environments

See merge request gitlab-org/gitlab-ce!15295

Fix blank states using old css

Closes #40377

See merge request gitlab-org/gitlab-ce!15521

Add wiki css to help page

See merge request gitlab-org/gitlab-ce!15488

This updates the composite index on ci_pipelines (project_id, ref,
status) to also include the "id" column at the end. Adding this column
to the index drastically improves the performance of queries used for
getting the latest pipeline for a particular branch. For example, on
project dashboards we'll run a query like the following:

    SELECT ci_pipelines.*
    FROM ci_pipelines
    WHERE ci_pipelines.project_id = 13083
    AND ci_pipelines.ref = 'master'
    AND ci_pipelines.status = 'success'
    ORDER BY ci_pipelines.id DESC
    LIMIT 1;

    Limit  (cost=0.43..58.88 rows=1 width=224) (actual time=26.956..26.956 rows=1 loops=1)
      Buffers: shared hit=6544 dirtied=16
      ->  Index Scan Backward using ci_pipelines_pkey on ci_pipelines  (cost=0.43..830922.89 rows=14216 width=224) (actual time=26.954..26.954 rows=1 loops=1)
            Filter: ((project_id = 13083) AND ((ref)::text = 'master'::text) AND ((status)::text = 'success'::text))
            Rows Removed by Filter: 6476
            Buffers: shared hit=6544 dirtied=16
    Planning time: 1.484 ms
    Execution time: 27.000 ms

Because of the lack of "id" in the index we end up scanning over the
primary key index, then applying a filter to filter out any remaining
rows. The more pipelines a GitLab instance has the slower this will get.

By adding "id" to the mentioned composite index we can change the above
plan into the following:

    Limit  (cost=0.56..2.01 rows=1 width=224) (actual time=0.034..0.034 rows=1 loops=1)
      Buffers: shared hit=5
      ->  Index Scan Backward using yorick_test on ci_pipelines  (cost=0.56..16326.37 rows=11243 width=224) (actual time=0.033..0.033 rows=1 loops=1)
            Index Cond: ((project_id = 13083) AND ((ref)::text = 'master'::text) AND ((status)::text = 'success'::text))
            Buffers: shared hit=5
    Planning time: 0.695 ms
    Execution time: 0.061 ms

This in turn leads to a best-case improvement of roughly 25
milliseconds, give or take a millisecond or two.

This changes Ci::Pipeline#latest_builds_with_artifacts so it returns an
Array instead of a relation. Whenever we use this data we do so in two
steps:

1. Count the number of rows
2. If this number is greater than 0, iterate over the rows

By returning an Array instead we only execute 1 query of which the total
time/work is less than running either just a COUNT(*) or both queries
(in the worst case).

On GitLab.com this change should save us a few milliseconds per request
to ProjectsController#show.

Optimize read-only middleware so that it does not consume as much CPU

Closes #40185 and gitlab-com/infrastructure#3240

See merge request gitlab-org/gitlab-ce!15504

Skip confirmation user api

Closes #28934

See merge request gitlab-org/gitlab-ce!15175

Custom issue tracker

See merge request gitlab-org/gitlab-ce!15516

Resolve "Notes API for issues no longer returns label additions/removals"

Closes #39461

See merge request gitlab-org/gitlab-ce!15080

Resolve "TagsPage|Tags"

Closes #40367

See merge request gitlab-org/gitlab-ce!15512

This reverts commit 91075c82.

Batch load blobs for diff generation

Closes #37599

See merge request gitlab-org/gitlab-ce!15370