Draft: Async content validation
Add async content validation hook for:
- after public project/wiki/snippet repository push commit.
- after change project/snippet visibility level to public or internal.
Split to blew MR:
- 
Add ContentBlockedStatemodel
- 
Add CommitService,ComplaintService,ContainerService,ProcessChangeService,CommitServiceWorker
- 
Add content_blocked_stateapi for add/remove state and user complaint
- 
Add controller and view template code 
- 
Add post_receive,importandupdate visibilitytrigger code
- 
Add content validation frontend components 
- 
Add i18n keys 
based Upstream MR:
Edited  by Linjie Zhang