Simplify variables validation in triggers API

See merge request !9506

Use correct GitLab Prometheus exporter name in docs

Closes #28619

See merge request !9503

Added application password instructions for Gmail/G suite accounts

See merge request !9486

Fix broken links in CI admin area docs

See merge request !9507

clarify Pages custom domain details

Closes #28577

See merge request !9457

Api remove owned groups

Closes #27937

See merge request !9505

Use persistent name identifier instead of transient in SAML2 documentation

Closes #28653

See merge request !9504

[ci skip]

# Conflicts:
#   doc/api/v3_to_v4.md

Return 202 with JSON body on async removals on V4 API

Closes #3874

See merge request !9449

Artifact Expiration Defaults

Closes #27762

See merge request !9219

Fixed instructions for adding Secret Variables to a CI/CD pipeline.

See merge request !9480

fixes job dropdown action button error

Closes #27530

See merge request !9182

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9219#note_24032923

* upstream/master: (247 commits)
  Switched CONTRIBUTING.md style guide recommendation for method chaining
  Fix new offenses
  Stylistic tweaks
  Fix OAuth/SAML user blocking behavior
  Revert "Enable Style/DotPosition"
  Revert "Prefer leading style for Style/DotPosition"
  Revert "Enable Style/BarePercentLiterals"
  Manually correct autocorrect
  Move up delegate calls
  Exclude migrations from Style/MutableConstant
  ActiveSupport delegation is preferred over Forwardable
  Update haml_lint to work with newest rubocop
  Add explanations to cops
  Update rubocop and rubocop-rspec and regenerate .rubocop_todo.yml
  Update rubocop and rubocop-rspec and regenerate .rubocop_todo.yml
  Order cops alphabetically
  Don’t exclude some file in lib from rubocop
  Fix new offenses
  Enable Rails/Delegate
  Enable Style/WordArray
  ...

Create master branch first if project is repository-less

Closes #26687

See merge request !9009

Disable unused tags count cache for Projects, Builds and Runners

Closes #27989

See merge request !9467

Enable the RSpec/BeEql cop

See merge request !9476

Fix white square and sidebar animation

Closes #28610

See merge request !9472

with 2-step verification.

Switched CONTRIBUTING.md style guide recommendation for method chaining

[ci skip]

See merge request !9483

Fix GitAccess specs

Closes #28620

See merge request !9479

Resolve "Test compiling frontend assets for production in CI"

Closes #28450

See merge request !9396

on branch deletion show loading icon and disabled the button

See merge request !6761

Enable (and disable) more RuboCops

See merge request !9432

Fix reprocessing skipped jobs when retrying pipeline

See merge request !9436

Use grape validation in the members API.

See merge request !9471

Use POST in the endpoint description for :resource/unsubscribe

See merge request !9469

Pages 0.3.2

See merge request !9474

Fix MR changes tab size count

Closes #27563

See merge request !9091