Break out host/port/username configurations

[visch]

No description provided.

[qbatten]

Dupe of #5, I think. I can push a PR for this if I get a ruling on whether we should

• allow either sqlalchemy_url or host/port/etc
• switch over only to host/port/etc and drop sqlalchemy_url altogether

I don't care either way. Here's a repost of my comment on 5:

Per @/aaronsteers comment here, should we drop the sqlalchemy_url option altogether? @/visch what do you think about that? Seems like the pro/con of allowing users to pass sqlalchemy_url is something like:

Pro: Flexible for users
Con: Leaves the tap with less control; could cause things to break if the tap upgrades driver and a user isn't aware of that

Sounds like either way we'll exclude the dialect+driver option in the broken-out configuration.

[aaronsteers]

Hi, @qbatten. We ran into this elsewhere also. While the connector is still young, this is the right time to make a breaking change and remove support for arbitrary sqlalchemy_url inputs. Overrides or additions to the base string could optionally be exposed as "extra_sqlalchemy_args" config option.

Driver-specific implementation choices should be abstracted away from the users, so that if we change the driver or certain implementation details without breaking (future) users.