`allowed_key_types` is removed and the `minimum_<type>_bits` fields are
renamed to `<tech>_key_restriction`. A special sentinel value (`-1`) signifies
that the key type is disabled.

This also feeds through to the UI - checkboxes per key type are out, inline
selection of "forbidden" and "allowed" (i.e., no restrictions) are in.

As with the previous model, unknown key types are disallowed, even if the
underlying ssh daemon happens to support them. The defaults have also been
changed from the lowest known bit size to "no restriction". So if someone
does happen to have a 768-bit RSA key, it will continue to work on upgrade, at
least until the administrator restricts them.

This is an amalgamation of:

* Cory Hinshaw: Initial implementation !5552
* Rémy Coutable: Updates !9350
* Nick Thomas: Resolve conflicts and add ED25519 support !13712

Increase z-index of dropdowns

Closes #36766 and #36866

See merge request !13889

Fix invalid attribute used for time-ago-tooltip component

Closes #37163

See merge request !13899

Update latest artifacts doc

See merge request !13924

Remove unwanted refs after importing a project

Closes #36807

See merge request !13766

Improve migrations using triggers

Closes #36633

See merge request !13666

Add time stats to Issue and Merge Request API

Closes #28453

See merge request !13335

Removed tooltips from new sidebar

Closes #35658

See merge request !13489

Update share project with groups docs

See merge request !13843

* upstream/master:
  Don't use public_send in destroy_conditionally! helper
  Fix MySQL failure for emoji autocomplete
  max-width for lazy-loaded images (this was removed in the original MR through merge resolution most probably)
  Replace 'project/user_lookup.feature' spinach test with an rspec analog
  Move GPG signed commits docs to new location

Closes #35658

Replace 'project/user_lookup.feature' spinach test with an rspec analog

See merge request !13863

Resolve "Mysql2::Error: Unknown column 'award_emoji.count' on master"

Closes #37231

See merge request !13926

Resolve "README.md: Header image scale not limited"

Closes #37058, #37024, and #37230

See merge request !13869

As we only override in two places, we could just ask for the value rather than
the method name.

Move GPG signed commits docs to new location

Closes #36804

See merge request !13872

* upstream/master: (225 commits)
  Add changelog entry
  Backports EE 2756 logic to CE.
  Make rubocop happy
  Make profile settings dropdown consistent
  Add filter by my reaction
  Update spec initialization with it being a shared component
  Update identicon path and selector
  Renamed to `identicon` and make shared component
  Merge branch 'master-i18n' into 'master'
  Fix broken Frontend JS guide
  Replace 'project/star.feature' spinach test with an rspec analog
  Adds position fixed to right sidebar
  Fixes the margin of the top buttons of the pipeline page
  Remove commented out code
  Better align fallback image emojis
  Decrease Metrics/CyclomaticComplexity threshold to 15
  Add changelog
  Respect the default visibility level when creating a group
  Further break with_repo_branch_commit into parts
  Make sure inspect doesn't generate crazy string
  ...

Update backup_restore.md documentation regarding S3 and IAM profiles.

See merge request !13871

Perf.slow issuable

Closes #32844

See merge request !13685

Improve AutocompleteController#users.json performance

Closes #36879

See merge request !13754

Postgres lets you treat `count` as another alias for `COUNT(*)` apparently, even
if that's not the actual alias used.

Fixes the margin of the top buttons of the pipeline page

Closes #34990

See merge request !13908

Respect the default visibility level when creating a group via the API

Closes #37198

See merge request !13903

API: Respect the 'If-Unmodified-Since' for delete endpoints

See merge request !9621

Make file template dropdowns consistent

See merge request !13577

Make profile settings dropdown consistent

See merge request !13623

Backports EE 2756 logic to CE.

See merge request !13892

Make notification dropdowns consistent

See merge request !13624

max-width for lazy-loaded images (this was removed in the original MR through merge resolution most probably)

Better align fallback image emojis

Closes #37147

See merge request !13881

Make Identicon for avatars a shared component

Closes #35010

See merge request !13919