* master: (94 commits)
  Merge branch 'open-redirect-fix-continue-to' into 'security'
  Merge branch 'open-redirect-host-fix' into 'security'
  Merge branch 'path-disclosure-proj-import-export' into 'security'
  Merge branch '29364-private-projects-mr-fix'
  Merge branch '30125-markdown-security'
  Issue title realtime
  Update CHANGELOG.md for 8.16.9
  Update CHANGELOG.md for 8.17.5
  Update CHANGELOG.md for 9.0.4
  Add "search" optional param and docs for V4
  Use PDFLab to render PDFs in GitLab
  Separate Scala from Java in CI examples
  Fix broken link
  Reorganize CI examples, add more links
  Refactor CI index page
  Remove deprecated field from workhorse response
  Use gitlab-workhorse 1.4.3
  Document how ETag caching middleware handles query parameters
  Make group skip validation in the frontend
  Use NamespaceValidator::WILDCARD_ROUTES in ETag caching middleware
  ...

Fix for open redirect vuln involving continue[to] params

See merge request !2083

Fix for three open redirect vulns using redirect_to url_for(params.merge)))

See merge request !2082

Fix for path disclosure in project import/export

See merge request !2080

Don’t show source project name when user does not have access

See merge request !2081

Remove class from SanitizationFilter whitelist

See merge request !2079

Issue title realtime

Closes #25051

See merge request !10115

[ci skip]

[ci skip]

[ci skip]

Deal with Rails autoload instance variable resets

See merge request !10338

Disable pipeline & environment actions that are not playable

Closes #25385 and #24601

See merge request !10052

Refactor CI index page

Closes #29217

See merge request !9861

Add "search" optional param and docs for V4

Closes #30195

See merge request !10358

Workhorse 1.4.3

Closes gitaly#167 and gitaly#177

See merge request !10479

Convert value to string before setting Poll-Interval header

See merge request !10477

Fix subgroup repository disappearance if group was moved

Closes #30261

See merge request !10414

Implement Gitaly refs client

See merge request !9291

Notice that this param is being supported since V3, but we have not added the proper docs for it

Removes the duplicated search icon in emoji menu

Closes #30416 and #30016

See merge request !10472

Render PDFs in GitLab

See merge request !10419

Document how ETag caching middleware handles query parameters

See merge request !10482

Use NamespaceValidator::WILDCARD_ROUTES in ETag caching middleware

See merge request !10478

Potential fix for intermittent spec failure in award emoji specs

Closes #30399

See merge request !10476

Load a preview of Sketch 43 files

See merge request !10470

Make group skip validation in the frontend

Closes #29236

See merge request !10426

NamespaceValidator::WILDCARD_ROUTES is less restrictive than
ProjectPathValidator::RESERVED and we really have to avoid only
routes that contain wildcard names.