Support "ApplicationName" connection parameter

[macripps]

With JDBC I can pass the ApplicationName parameter as part of the connection string - jdbc:postgresql://localhost:5435/DBNAME?ApplicationName=MyApp - and have "MyApp" show up in various statistics on the server. It would be useful to be able to do this on finagle-postgres as well.

[leonmaia]

Thanks, @agenticarus. I would happily ship this change in case you have time to work on this. If you don't have the time it can take a while since we right now don't have a lot of people maintaining this project, and there are some big upgrades and fixes with more priority in the backlog.

[macripps]

I'll take a look!