Improve Handling of replay_lsn for Idle Source (#519)

Prior to this commit, the replay_lsn remained static when the source was idle
for an extended period, potentially leading to inaccurate replication lag
monitoring. This commit addresses this issue by ensuring the replay_lsn is
updated consistently, even when the source is idle, providing a more accurate
reflection of the system's state.

Signed-off-by: Arunprasad Rajkumar <ar.arunprasad@gmail.com>