Expanded logical replication support

[justinwyer]

Hi @porsager would you be open to expanding the logical replication implementation to:

1. Allow the passing of a pre-existing replication slot name and LSN start point?
2. Passing the LSN to the subscriber

If so I'll start work on a PR.

[porsager]

Yes! That'd be great 👍

[coder-se]

Hi @justinwyer did you end up working on this? Would love to see this in postgres.js, I've been researching for alternatives but haven't found any that's up-to-date.

[justinwyer]

@coder-se I did do some work on it, but got distracted making a batteries included test setup as another contribution, subsequently my daughter has arrived and I've temporarily moved off of our PostgreSQL effort at work. It's still very much on my to-do list however.