Upgrade to Rails 6

Closes #30030 and #31034

See merge request gitlab-org/gitlab!19891

Fix Geo Sidebar missing `active` class

Closes #199238

See merge request gitlab-org/gitlab!23885

Spec

Tests and lint

Move the clone button to the tree controls area

See merge request gitlab-org/gitlab!17752

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/17752

Create backend route for dedicated Release page

See merge request gitlab-org/gitlab!23792

Remove existing to clarify examples

See merge request gitlab-org/gitlab!23987

Refactor merge request routing

See merge request gitlab-org/gitlab!23782

Added Monaco-based editor lite version

Closes #198618

See merge request gitlab-org/gitlab!23767

This introduces the bare-minimum Monaco editor for single-file edits
like those for Snippets, blobs and CI/CD configurations

Merge branch '197973-staged-and-unstaged-modification-tooltip-for-file-with-staged-changes-in-web-ide' into 'master'

Resolve "Staged and unstaged modification" tooltip

See merge request gitlab-org/gitlab!23847

When credentials are changed, the field isn't marked as dirty
which results in the model not being saved or updated.

The query was passing a string for file_type when it is an int.
This is actually an unused column but was working in Rails 5
because it was just coerced to 0 which is the default value.

In Rails 6, it is now nil so no records match our query

In Rails 6, after_commit callbacks are no longer called
unless the model was saved

The behavior of this is going to change in Rails 6.1
where.not(a: 1, b: 2) is going to be:

WHERE (a != 1 OR b !=2 ) instead of WHERE (a != 1 AND b != 2)

Previously, having the `where` turned this into a relation
so `ActiveRecord::Relation#delete_all` is called.

In Rails 6, `ActiveRecord::Associations::CollectionProxy#delete_all`
is called causing an error in the query.

* Disable locking at the class-level for `update_all`

* Fixes DEPRECATION WARNING: `ActiveRecord::Result#to_hash` has been
  renamed to `to_a`. `to_hash` is deprecated and will be removed in
  Rails 6.1.

* Fix lookup of CE views

  `view_paths=` was removed so we just create a new LookupContext
  here instead of duplicating then modifying the paths

* Fix some view related spec failures

* Fix database configuration for connection pools

  ActiveRecord::Base.configurations now returns a
  ActiveRecord::DatabaseConfigurations object

We use `present_members` here so that associations are preloaded.
We do this even if there's only one record here because it raises
an exception when user.status isn't preloaded.

In Rails 6, content_type now returns the complete header. We use
media_type to just get the MIME type portion

See https://github.com/rails/rails/pull/36034

Removes patches that are already in Rails 6:
Gitlab::ContentDisposition patch
ActiveRecord::QueryCache patch
ActiveJob::Arguments patch
Gitlab::ActionViewOutput patch

Updates Activerecord::Locking::Optimistic patch to follow changes in
https://github.com/rails/rails/blob/v6.0.1/activerecord/lib/active_record/locking/optimistic.rb

Fix missing timezone for datetime_with_timezone by adding this custom
type to ActiveRecord's time_zone_aware_attributes

There are also minor changes to keep the Rails generated files
similar to when generating a new Rails 6 application

grape_logging was upgraded to fix deprecation messages related to
ActionDispatch::Http::ParameterFilter

Rails 6 now adds the nonce to style-src by default. We disable
this because we still have a lot of code that set inline styles
and we need 'unsafe-inline'

Move SpamCheckService into spam folder

See merge request gitlab-org/gitlab!23915

Support design repo in project namespace transfer

See merge request gitlab-org/gitlab!23573

This commit adds the backend route for the dedicated release show page.
This page is hidden behind a `release_show_page` feature flag which is
disabled by default.

Delete a comment

See merge request gitlab-org/gitlab!23937

Add a `class_name: "::Project"` to a `belongs_to :project` in a spec

Closes #199424

See merge request gitlab-org/gitlab!23979

Merge branch '39505-extend-the-ability-to-clone-a-dashboard-so-it-would-copy-the-custom-metrics' into 'master'

Extend the ability to clone a dashboard so it would copy the custom metrics

See merge request gitlab-org/gitlab!21923

Fix missing 'Pipeline schedules' link

Closes #199088

See merge request gitlab-org/gitlab!23842

- Add test case for FOSS and EE project and group navbar structure.

Feature flag: adding of use_core_delta_islands

See merge request gitlab-org/gitlab!23850

Remove Elastic Stack cluster application feature flag

See merge request gitlab-org/gitlab!23058

Enable the app by default

To make metrics dashboard clonning fully function, we need to inclued
custom metrics defined by user.

Update Dependency Proxy to ultimate only

See merge request gitlab-org/gitlab!23925

update link to BATS

See merge request gitlab-org/gitlab!23866