Models and migrations for group level clusters

See merge request gitlab-org/gitlab-ce!22307

Add None/Any options for assignee in search bar

Closes #52383

See merge request gitlab-org/gitlab-ce!22599

Backport CE route changes for Ops Dashboard in EE

See merge request gitlab-org/gitlab-ce!22640

Fixing count on Milestones

Closes #50848

See merge request gitlab-org/gitlab-ce!21446

Merge branch '52780-stale-pipeline-status-cache-for-_project-after-disabling-pipelines' into 'master'

Resolve "Stale pipeline status cache for `_project` after disabling pipelines"

Closes #52780

See merge request gitlab-org/gitlab-ce!22589

Even though we currently only should have one group for a cluster, we
allow the flexibility to associate to other groups in the future.

This also matches the runner <=> groups association.

- Adds Cluster#first_group, aliased to Cluster#group. For the
conceivable future, a cluster will have at most one group.

- Prevent mixing of group and project clusters. If project type
clusters, it should only have projects assigned.  Similarly with groups.

- Default cluster_type to :project_type. As it's very small table we can
set default and null: false in one release.

Update links to external sites

See merge request gitlab-org/gitlab-ce!22578

Add failure reason for execution timeout

See merge request gitlab-org/gitlab-ce!22224

remove duplicate section for enabling at project level

See merge request gitlab-org/gitlab-ce!22627

User not defined in PostReceive#process_project_changes

Closes #51335

See merge request gitlab-org/gitlab-ce!22519

Adds trace of each access check when git push times out

Closes #42790

See merge request gitlab-org/gitlab-ce!22265

Upgrade Prometheus to 2.4.3 and Alertmanager to 0.15.2

See merge request gitlab-org/gitlab-ce!22600

docs add first draft for runbook topic

See merge request gitlab-org/gitlab-ce!22588

# Conflicts:
#	doc/topics/runbooks/index.md

Update review apps testing guide

See merge request gitlab-org/gitlab-ce!22619

E2E Test - LDAP login with SSL

Closes gitlab-qa#59

See merge request gitlab-org/gitlab-ce!22574

Prettify all the things (part 4)

See merge request gitlab-org/gitlab-ce!22253

Resolve circular dependencies in merge request widget

See merge request gitlab-org/gitlab-ce!22605

Resolve "No longer require a deploy to start Prometheus monitoring"

Closes #45068

See merge request gitlab-org/gitlab-ce!22401

Review Apps are now deployed automatically.
Note that if auth fails you might need to stop and redeploy the app.

Feature/add license to project API

See merge request gitlab-org/gitlab-ce!21606

Update content of visible tooltips

See merge request gitlab-org/gitlab-ce!22504

CE: Put EE routes in EE files under EE directories

See merge request gitlab-org/gitlab-ce!22376

Automatically navigate to last board visited

See merge request gitlab-org/gitlab-ce!22430