Since the migration might be queued already and be rescheduled when it
fails on a uniqueness error, this should help clearing the background
migration queue faster.
This adds a Rubocop configuration file specific to
lib/gitlab/background_migrations. This configuration will be used to
(hopefully) make reviewing background migrations easier by enforcing
stricter rules compared to the rest of GitLab. Because this
configuration is directory specific it will only affect background
migrations.
In case the root project of a Fork-of-fork is deleted, the ForkNetwork
and the membership for that fork network is never created. In this
case we shouldn't try to create the membership, since the parent
membership will never be created.
This means that these fork networks will be lost.