[10.3] Migrate `can_push` column from `keys` to `deploy_keys_project`
See merge request gitlab/gitlabhq!2276
(cherry picked from commit f6ca52d31bac350a23938e0aebf717c767b4710c)
1f2bd3c0 Backport to 10.3
Added specs for the deploy_keys_presenter and added a new method in the presenter
called #key_available?
Fixed some minor UX inconsistencies and added a concern to handle
redirection