Geo: Improvements and fixes after QA

We are going to move Geo (#76) to General Availability. This MR will handle all small fixes and changes to get a solid release

- [x] Replicates repository removal (using system hooks)
- [x] Replicates repository rename (using system hooks)
- [x] Replicates repository transfer (using system hooks)
- [x] Whitelisted Sidekiq routes so you can use web interface in a secondary node.
- [x] Change "Gitlab -> GitLab" for the readonly error flash
- [x] Check license add-on to allow any Geo features. 
- [x] Do not execute on a secondary node: `StuckCiBuildsWorker`
- [x] Do not execute on a secondary node: `HistoricalDataWorker`
- [x] Documentation changes: (master, slave -> primary, secondary)
- [x] Document we require `db_key_base`(secrets.yml) to be the same in all nodes

See merge request !354

Mark 8.7.0 as released



See merge request !358

[ci skip]

Refactor update documentation

Port from CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3822

See merge request !355

[ci skip]

[ci skip]

Geo development documentation

Added some developer oriented documentation for Geo feature (#76)

See merge request !350

Geo: repository sync changed to use push event from system hook

Changed from our own custom implementation, to use GitLab's system hook push event to trigger repository synchronization for Geo (#76). 

See merge request !347

CE upstream



See merge request !348

Sync CE master to EE master



See merge request !346

Add notice about GitLab Runner to requirements docs

This is related to #14589, and problems that may stem from running
GitLab Runner on same machine user installed GitLab web app on.

See merge request !3518

Add configurable shared runners text

cc @axil @rspeicher @grzesiek 

See merge request !3750

* 'master' of dev.gitlab.org:gitlab/gitlabhq:
  Add Changelog entry for group link permissions fix
  Use guard clause to check ability to share project
  Refactor method that shares project with a group
  Check permissions when sharing project with group

Check permissions when sharing project with group

## Summary

Unprivileged user was able to share project with group he didn't have access to, and therefore gain partial access to that group, which opened possibilities for further actions like listing private projects in that group.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/15330

## Fix

This change introduces additional check for group read access.

## Further work

We can think about preventing such problems in the future (this is quite common problem) by moving permissions checks to another layer of abstraction (TBD).

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15330

See merge request !1949

Make before_script and after_script overridable

This is makes it possible to overwrite the before_script and after_script at job level.

This is continuation of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3771


See merge request !3772

Implement after_script which allows to do cleanups as part of the build process

This implements `after_script` in global context.

The `after_script` will be executed always after the job, even if the job were canceled.

This requires changes on Runner side that will be implemented in 1.2.

cc @tmaczukin @grzesiek 


See merge request !3771

Allow enable/disable push events for system hooks in UI

Improvement for !3744 

Fixes #15284 

See merge request !3812