feat: support connecting to different databases

[olavloite]

Support connecting to different databases on an instance. This allows
for the use of the \c command in psql, as well as using a single
instance of PGAdapter to connect to multiple different databases using
other clients. The -d command line parameter is still supported, but
is now interpreted as follows:

1. If omitted, PGAdapter will connect to the database given in the
   connection request.
2. If included, PGAdapter will always connect to the database given in
   the -d command line parameter and ignore the database in the
   connection request.

Fixes b/194320320

[aseering]

Do I understand correctly that this is a "breaking change" in the sense that, if customers relied on PGAdapter's behavior of ignoring the database specified by psql (which is pretty easy to do, for example with scripts that assume they can connect to the postgres default database to do admin operations), previously they might have worked and now they won't?

If so, could this be accompanied by a bump to PGAdapter's published major version? That would be a minimal way to signal a breaking change.

[olavloite]

Do I understand correctly that this is a "breaking change" in the sense that, if customers relied on PGAdapter's behavior of ignoring the database specified by psql (which is pretty easy to do, for example with scripts that assume they can connect to the postgres default database to do admin operations), previously they might have worked and now they won't?

If so, could this be accompanied by a bump to PGAdapter's published major version? That would be a minimal way to signal a breaking change.

No, I think either my comment was not clear enough or you did not read that correctly :-)

The behavior is:

1. If you continue to start PGAdapter with the -d command: The behavior remains exactly as it is now. The database name in the connection request is always ignored.
2. If you omit the -d command: PGAdapter will always use the database name in the connection request.

Note that the -d command was required. This PR changes that and makes it optional. So there is currently no one who can be using PGAdapter without the -d command.

[aseering]

Ah, I see: In your original statement, when reading:

If included, PGAdapter will always connect to the database given in
the -d command line parameter and ignore the database in the
connection request.

I interpreted that as the -d argument to psql. I think you actually meant the -d argument to PGAdapter? Which in retrospect should have been evident from context; I just mis-parsed.

Anyway, agreed, SGTM.