Upgrade Ruby to 2.3.5

See merge request gitlab-org/gitlab-ce!15099

Improve the maintenance policy page

See merge request gitlab-org/gitlab-ce!15112

Load participants async

Closes #23206

See merge request gitlab-org/gitlab-ce!14836

Fix missing issue assignees

Closes #39170

See merge request gitlab-org/gitlab-ce!15109

Make clear that we may backport bug fixes to the previous stable
release.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix overlap of right-sidebar and wiki create page form

Closes #39509

See merge request gitlab-org/gitlab-ce!15075

Adds project_id to pipeline hook data

Closes #31454

See merge request gitlab-org/gitlab-ce!15044

Allow promoting project milestones to group milestones

Closes #38777

See merge request gitlab-org/gitlab-ce!14831

Migrate Gitlab::Git::Wiki#delete_page to Gitaly

Closes gitaly#673

See merge request gitlab-org/gitlab-ce!14910

Handle large values on `MergeRequestDiffCommit` dates

Closes #39561

See merge request gitlab-org/gitlab-ce!15093

Fix example typo.

See merge request gitlab-org/gitlab-ce!15104

Signed-off-by: Rémy Coutable <remy@rymai.me>

Part of gitlab-org/gitlab-ce#38040

Remove issue and issue status select from global namespace

See merge request gitlab-org/gitlab-ce!15090

Hashed Storage support for Attachments

See merge request gitlab-org/gitlab-ce!15068

Adds callback function to initial cluster request

Closes #39639

See merge request gitlab-org/gitlab-ce!15105

Fix namespacing for MergeWhenPipelineSucceedsService in MR API

Closes #39619

See merge request gitlab-org/gitlab-ce!15088

Add Packagist project service

See merge request gitlab-org/gitlab-ce!14493

Closes gitaly#673

Upload files through the multi-file editor

Closes #38629 and #38614

See merge request gitlab-org/gitlab-ce!14975

Merge branch '39593-emails-on-push-are-sent-to-only-the-first-recipient-when-using-aws-ses' into 'master'

Resolve "Emails on Push are sent to only the first recipient when using AWS SES"

Closes #39593

See merge request gitlab-org/gitlab-ce!15083

Resolve "Convert autosize.js library to be a Yarn managed library"

Closes #39616

See merge request gitlab-org/gitlab-ce!15087

Revert "Merge branch '2518-saved-configuration-for-issue-board' into 'master'"

See merge request gitlab-org/gitlab-ce!15092

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/39509

Pipeline hook data now includes the project_id

This reverts merge request !15009