GitLab

Previously when performing a write we would stick to the primary for the
duration of a request. This could lead to unnecessary pressure on the
primary database.

To work around this we stop using the primary the moment all secondaries
are in sync with the last write. If we are in an explicit transaction we
will keep using the primary until the transaction finishes.

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/6041