This adds various foreign key constraints, indexes, missing NOT NULL
constraints, and changes some column types from timestamp to
timestamptz.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/31811

also, I refactored the MergeRequest#fetch_ref method to express
the side-effect that this method has.

  MergeRequest#fetch_ref -> MergeRequest#fetch_ref!
  Repository#fetch_source_branch -> Repository#fetch_source_branch!

We already had this the other way around (merge_request_diffs.merge_request_id),
but this is needed to gather only the most recent diffs for a set of merge
requests.

Fix out of sync with KubernetesService. Remove namespace pramas from controller. Use time_with_zone in schema. Remove Gcp::Clusters from safe_model_attributes.ym

When no fork network exists for the source projects, we create a new
one with the correct source

The fork network will keep track of the root project as long as it's
present.

Additionally we're delegating missing method calls on GpgKeySubkey to
GpgKey since most of the info required when verifying a signature is
found on GpgKey which is the parent of GpgKeySubkey

Conflicts:
	db/schema.rb