https://gitlab.com/gitlab-org/gitlab/-/merge_requests/42435 attempted to
fix the problem, but it did not work because EE databaase load balancing
is not enabled in Sidekiq. Since it is disabled, the load balancer code
would never post the write location to Redis, so the code for checking
whether to stick to the primary was not able to be used.

Since Sidekiq always uses the primary we can just use the main
ActiveRecord connection to get the same information. We only post the
write location if load balancing is configured.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/247857