Extend Gitlab::Database::LoadBalancing modules to track individual load-balancer primary/replica usage status

This issue is created out of #3805 (closed).

We will track the efforts to update the Gitlab::Database::LoadBalancing modules in gitlab rails to:

• track Gitlab::Database::LoadBalancing::ConnectionProxy usage of primary/replica
• track connections for databases undergoing decomposition (gitlab-org&14165 (closed))

Tracking individual database connection proxy's primary/replica usage status unblocks work in &1414