Add a user-facing log/status indicator for locked slot creation during initial load

[Amogh-Bharadwaj]

In certain busy databases, the create_replication command which we run during our initial load+cdc workloads can get locked. During this time, the UI is dead and does not give visibility to the user. This locked state can take as long as an hour.

Make PeerDB cognisant of locked initial loads and relay the information via the API to clients