Re-expose `model.connection.load_balancer` to have LB of the connection

What does this MR do and why?

Re-expose model.connection.load_balancer to have LB of the connection

The is required by pg_wal_lsn_diff to execute against closest connection to compare WAL pointers.

Without that it causes duplicate_job to fail on unable to call model.connection.load_balancer.wal_diff.

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