Backport New SystemHook: `repository_update`

Closes #26325

See merge request !11140

[ci skip]

[ci skip]

Wait for requests after each Spinach scenario instead of feature

See merge request !11349

[ci skip]

[ci skip]

Link to a case where we can't support MySQL

Closes #32181

See merge request !11334

Remove trailing comma in dependency linker to satisfy Rubocop

See merge request !11348

Add fixed positioning to top level navbar

Closes #30975

See merge request !10751

Relax rake backup regex to handle CE and EE RCs

See merge request !11345

Fix conflict resolution from corrupted upstream

Closes gitlab-ee#2128

See merge request !11298

New branch new mr docs

See merge request !11308

See http://rubular.com/r/uTDlT85zW1

I don't know why this happens exactly, but given an upstream and fork repository
from a customer, both of which required GC, resolving conflicts would corrupt
the fork so badly that it couldn't be cloned.

This isn't a perfect fix for that case, because the MR may still need to be
merged manually, but it does ensure that the repository is at least usable.

My best guess is that when we generate the index for the conflict
resolution (which we previously did in the target project), we obtain a
reference to an OID that doesn't exist in the source, even though we already
fetch the refs from the target into the source.

Explicitly setting the source project as the place to get the merge index from
seems to prevent repository corruption in this way.

Usage ping updates

Closes #31741 and #31453

See merge request !11231

Improve project list cache key

Closes #31863

See merge request !11325

Autolink package names in Gemfile

See merge request !11224

Paste a copied MR source branch name as code when pasted into a GFM form

See merge request !11315

Removed all instances of Object.assign by using es6 classes, also includes some …

See merge request !11288

Expose memory deltas between app deployments and refactor prometheus queries to support more custom queries

See merge request !10981

Only rename namespaces and projects with an invalid path

See merge request !11338

# Conflicts:
#   app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.js

Consistently use monospace font for commit SHAs and branch and tag names

See merge request !11276

Fix form_spec.rb

See merge request !11330