Integrates frontend with API to enable
attaching epics to an epic

Add controller + services for:
 - setting a parent
 - list epics
 - delete associarion

Adds backstage support to related issues app
to enable attaching epics to an epic

Remove epics field for projects not in groups

Closes #7866

See merge request gitlab-org/gitlab-ee!8919

Add missing entries to locale/gitlab.pot

Closes #8940

See merge request gitlab-org/gitlab-ee!8935

Also fixes epics field being shown in MRs

CE port: Rename GroupHierarchy into ObjectHierarchy

See merge request gitlab-org/gitlab-ce!23923

restores changes from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23816

Resolve "Add tests for "Redesign projects lists UI""

Closes #55359

See merge request gitlab-org/gitlab-ce!23915

Fix sidekiq-reliable-fetch version

Closes sidekiq-reliable-fetch#18

See merge request gitlab-org/gitlab-ce!23937

Removed pipeline_ci_sources_only feature flag

See merge request gitlab-org/gitlab-ce!23926

Upgrade @gitlab/ui to 1.16.2

See merge request gitlab-org/gitlab-ce!23946

Cache avatar URLs and paths within a request

Closes #55355

See merge request gitlab-org/gitlab-ce!23950

Resolve "Hide cluster features that don't work yet with Group Clusters"

Closes #55103

See merge request gitlab-org/gitlab-ce!23935

Merge branch '51606-expanding-a-diff-while-having-an-open-comment-form-will-always-scroll-down-to-the-comment' into 'master'

Resolve "Expanding a diff while having an open comment form will always scroll down to the comment"

Closes #51606

See merge request gitlab-org/gitlab-ce!23849

Adds Vuex Store for the releases page

See merge request gitlab-org/gitlab-ce!23796

[EE Port] Adds Vuex Store for the releases page

See merge request gitlab-org/gitlab-ee!8911

Resolve "Sidebar styling updates"

Closes #54814

See merge request gitlab-org/gitlab-ce!23816

Resolve "Adapt subscriptions page for free plans and trials"

Closes #8838

See merge request gitlab-org/gitlab-ee!8838

Resolve "Hide cluster features that don't work yet with Group Clusters"

See merge request gitlab-org/gitlab-ee!8924

Replace outer padding of issue boards switcher with margin

See merge request gitlab-org/gitlab-ee!8929

Dismiss epic promotion and persist across reload

See merge request gitlab-org/gitlab-ee!8885

Remove duplicate padding from issue board switcher

Closes #8937

See merge request gitlab-org/gitlab-ee!8928

In a merge request with many discussions, the avatar URL can be called
thousands of times, inflicting a significant performance penalty
especially when avatars are stored in object storage. To mitigate this
problem, we can just cache the generated path any time it is requested.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/55355

Refactor the pipelines for merge requests docs

See merge request gitlab-org/gitlab-ce!23905

SSH docs: clarify that you need to accept the authenticity of the server

Closes #54880

See merge request gitlab-org/gitlab-ce!23584