Docs: Correct upgrade guides for 12.0

See merge request gitlab-org/gitlab-ce!29846

It's fine to upgrade from 11.11.x to 12.x, so we remove the requirement
to first upgrade to 12.0.x.

Merge branch '63399-intermittent-spec-failure-in-spec-models-ci-pipeline_schedule_spec-rb-131' into 'master'

Resolve "Intermittent spec failure in spec/models/ci/pipeline_schedule_spec.rb:131"

Closes #63399

See merge request gitlab-org/gitlab-ce!29838

Refactor file locking docs

See merge request gitlab-org/gitlab-ce!29686

- Remove outdated 'introduced in' section
- Update/remove images

Fixes flaky master

Unquarantine the branches E2E test

Closes gitlab-org/quality/nightly#62

See merge request gitlab-org/gitlab-ce!29828

Docs: Added source upgrade guides for 12.0.0

See merge request gitlab-org/gitlab-ce!29795

Document Usage Quotas group settings page

Closes #63022

See merge request gitlab-org/gitlab-ce!29599

Add zoom call section in issue data page

See merge request gitlab-org/gitlab-ce!29815

Add changelog entry for the new operations_feature_flags_clients.token_encrypted column

See merge request gitlab-org/gitlab-ce!29820

We missed to add this in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29320.

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/57918

Unquarantine merge tests

Closes gitlab-org/quality/nightly#93 and gitlab-org/quality/nightly#94

See merge request gitlab-org/gitlab-ce!29833

Crosslink Mattermost integrations, simplify components list

See merge request gitlab-org/gitlab-ce!29317

Allow developers to delete tags

Closes #52954

See merge request gitlab-org/gitlab-ce!29668

This commit adds
 - feature specs
  - to test the ability of a user with "developer" permission
    to delete tags in repositories.
 - documentation

Fix Container Scanning job with K8S runners

Closes gitlab-ee#11448

See merge request gitlab-org/gitlab-ce!29706

Add note about not translating API messages.

See merge request gitlab-org/gitlab-ce!29748

Add identity information to external authorization requests

See merge request gitlab-org/gitlab-ce!29461

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/61201#

Fix missing API notification flags for Microsoft Teams

See merge request gitlab-org/gitlab-ce!29824

Demote new section

See merge request gitlab-org/gitlab-ce!29829

Un-quarantine OAuth spec

Closes gitlab-org/quality/nightly#100

See merge request gitlab-org/gitlab-ce!29764

Remove support for app label matching

See merge request gitlab-org/gitlab-ce!29460

Removes database.yml.example

See merge request gitlab-org/gitlab-ce!29822

It's an empty file that was committed by accident on
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28565

From now on, only match on the annotations, instead of falling back to
legacy app label. This enables users to use the app label for other
purposes such as helm charts.