GitLab Pages: new guides

Closes #28097, gitlab-ee#994, #28098, and #28190

See merge request !9395

Remove require.context from cycle_analytics_bundle

See merge request !9393

Present GitLab version for each V3 to V4 API change on v3_to_v4.md

Closes #28458

See merge request !9425

Allow setting of a custom connection pool host

See merge request !9445

Custom brand header logo in emails

Closes #24969 and #25570

See merge request !9049

Add merge request count to each issue on issues list

Closes #19786 and #23208

See merge request !9252

Add housekeeping endpoint for Projects API

Closes #27032

See merge request !9421

Similar to changelog, mention the Merge Request id & link for each
change.

Chat slash commands show labels correctly

Closes #28358

See merge request !9408

Document when current coverage configuration option was introduced

Closes #28524

See merge request !9443

Improves the environments list action buttons

Closes #24651

See merge request !9424

Update two_factor_authentication.md by correcting FreeOTP link.

See merge request !9368

Grapify the CI::Runners API

See merge request !9440

This allows you to set a custom host when calling
Gitlab::Database.create_connection_pool. This is necessary for load
balancing as in this case we want to inherit all settings except for the
hostname.

[ci skip]

UI: Allow a project variable to be set to an empty value

See merge request !9414

Grapfiy the CI::Triggers API

See merge request !9439

Add AsciiDoc snippet for CI/CD Badges

Closes #26087

See merge request !9164

docs(ci/docker_build): Add example of variable use

See merge request !9159

* Introduced in v8.17

[skip ci]

Standardize branch name params as `branch` on V4 API

Closes #22132

See merge request !8936

API: Make subscription API more RESTfuL

Closes #28327

See merge request !9325