Add support to modify and ignore incoming connection parameters

[bentsku]

This PR allows the proxy to modify and ignore the incoming connection parameters, allowing for example Redshift connector to connect to a Postgres server. A release on pypi will be needed.

List of allowed connection parameters: https://www.postgresql.org/docs/11/libpq-connect.html#LIBPQ-PARAMKEYWORDS

[dfangl]

LGTM! At some point we might need to introduce a handler for connection requests as well, but this seems good so far!

We will have to see if keeping the whitelist up to date takes a lot of work or not.

[dfangl]

We probably have to adjust this list for each new postgresql version, but seems like a good solution for now!

[bentsku]

Yes, I thought about either going through a modular approach for connection handlers, or instead setting it directly. As we only have postgres after our proxy, I thought it could be done directly for now, but not closing any doors!
For the whitelist, I made a small script fetching and parsing the postgres documentation page linked above, so it is pretty fast but needs to be thought about, that's a thing.

[whummer]

Nice set of changes @bentsku 👍 - great detective work! 🔍