Add support for databases with encodings other than UTF-8/16/32

We should test with a Postgres database that uses another encoding than UTF-8/16/32. I'm not sure how that'd be handled by the ProtoBuf plug-in, but with wal2json I'd expect things not to work, as Jackson can only handle these encodings automatically. Worth exploring whether it can even be made work with other encodings via wal2json. It sends messages based on the server's encoding as per this thread, so one approach may be to query for the server's encoding and apply that when processing incoming events.

If there are limitations in terms of supported encodings, we should make them clear in the connector docs.