Backport 5480-epic-notifications from EE

See merge request gitlab-org/gitlab-ce!18724

Upgrade to Webpack 4

Closes #43400

See merge request gitlab-org/gitlab-ce!17218

Fix close keyboard shortcuts dialog using the keyboard shortcut

See merge request gitlab-org/gitlab-ce!18783

Make deploy keys table more clearly structured

Closes #41082

See merge request gitlab-org/gitlab-ce!18279

Resolve "Inform users of up to $500 offer for GCP account"

Closes #43469

See merge request gitlab-org/gitlab-ce!18684

Add notice to current fe guide about new fe guide

Closes #46067

See merge request gitlab-org/gitlab-ce!18781

Resolve "Issue Boards List Heading Label chooses Wrong Text Color"

Closes #36983

See merge request gitlab-org/gitlab-ce!18786

* master: (252 commits)
  Upgrade underscore.js
  Enable prometheus metrics by default
  Add signature verification badge to compare view
  Add Changelog
  Update instalation from source guide
  fix Web IDE file tree scroll issue
  Enable quick support actions default
  Backport of 4084-epics-username-autocomplete
  Remove top margin on the terms page with performance bar
  Backports every CE related change from ee-44542 to CE
  Fix typo in changelog entry
  fix missing space
  Backport IdentityLinker#failed? from GroupSaml callback flow
  Add ci_cd_settings delete_all dependency on project
  AutoDevOps Docs fix invalid external link
  Ignore knapsack and rspec_flaky
  Ensure web hook 'blocked URL' errors are stored in as web hook logs and properly surfaced to the user
  Partially revert ebcd5711 to fix runner pages
  Reuses `InternalRedirect` when possible
  Enforces terms in the web application
  ...

Resolve "Clean up bottom status bar Web IDE"

Closes #44833

See merge request gitlab-org/gitlab-ce!18756

Add update guide for 10.8

See merge request gitlab-org/gitlab-ce!18695

Improved commit message body rendering

See merge request gitlab-org/gitlab-ce!18725

Backport of 1481-changing-weight-values-should-trigger-system-notes

See merge request gitlab-org/gitlab-ce!18699

Add CI_COMMIT_MESSAGE, CI_COMMIT_TITLE and CI_COMMIT_DESCRIPTION predefined variables

Closes #20400

See merge request gitlab-org/gitlab-ce!18672

Improve UX For Group Runners

See merge request gitlab-org/gitlab-ce!18649

CE backport of Backports Push Mirrors to CE

Closes #42099

See merge request gitlab-org/gitlab-ce!18715

Cleanup pipeline build stage background migration

Closes #43854

See merge request gitlab-org/gitlab-ce!18778

Fix nginx metric names

Closes #45163

See merge request gitlab-org/gitlab-ce!18770

Client implementation GetRawChanges

See merge request gitlab-org/gitlab-ce!18693

Fix a couple of things in the security template for developers

See merge request gitlab-org/gitlab-ce!18776

Bump Gitaly to 0.98.0

See merge request gitlab-org/gitlab-ce!18740