Based on BE reviewer feedback

As the frontend is still in progress and other related backend is still
in prgress we need a feature flag to turn off Group Clusters.

These applications will need further work in future issues to enable
them to work with groups of projects.

Remove the requirement to have actual_namespace before using kubeclient.

- Add pages javascripts to intialize clusters for group pages

- Move specs asserting gcp specific validations from controller into
UpdateService spec

- Also teach Clusters::ApplicationController about groups

As this is the only item in this menu, make Kubernetes the link for the
sidebar item too.

- maintainer for group can read, create, update, and admin cluster
- project user, at any level, cannot do anything with group cluster

Fix for the filter spec failure

Closes gitlab-org/quality/nightly#34 and gitlab-org/quality/nightly#30

See merge request gitlab-org/gitlab-ce!22862

Adds documentation for restricted project service account in deployment jobs

Closes #51717

See merge request gitlab-org/gitlab-ce!22810

Document that we do not support importing bare repositories from hashed storage in certain cases

Closes #41423

See merge request gitlab-org/gitlab-ce!22783

Add e2e test of push over SSH using Git protocol v2

See merge request gitlab-org/gitlab-ce!22548

Emphasis the importance of auth registry

See merge request gitlab-org/gitlab-ce!22843

StuckImportJobsWorker query performance optimization

See merge request gitlab-org/gitlab-ce!22879

Adds a btn-icon class

See merge request gitlab-org/gitlab-ce!22870

Align sign in button

Closes #53673

See merge request gitlab-org/gitlab-ce!22888

Improves the performance of fetching the enqueued
projects for StuckImportJobsWorker, preventing a
statement timeout.

Prevent attr_encrypted models from being overriden

Closes gitlab-ee#8234

See merge request gitlab-org/gitlab-ce!22764

Paginate Bitbucket Server importer projects

See merge request gitlab-org/gitlab-ce!22825

Fix failing spec in spec/controllers/admin/hooks_controller_spec.rb

attr_encrypted expects models to have their attribute methods defined,
or it will override them with standard Ruby accessors. Migration specs
that rolled back the state of the database after columns were migrated
to encrypted values were interfering with these definitions. To ensure
that the SystemHook specs pass, we need to call
`SystemHook.define_attribute_methods` to ensure that attr_encrypted sees
the right methods that reflect the latest state of the database.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/8234

Warn when MR titles are too long.

See merge request gitlab-org/gitlab-ce!22845

Usage ping - Differentiate Jira Server and Cloud

Closes #51043

See merge request gitlab-org/gitlab-ce!22791

Fix e2e create merge request test

Closes gitlab-org/quality/nightly#32

See merge request gitlab-org/gitlab-ce!22877

To prevent delays in loading the page and reduce memory usage, limit the
number of projects shown at 25 per page.

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/50021

Allow to add patches to merge requests created via email

Closes #40830

See merge request gitlab-org/gitlab-ce!22723