Implement new "connections" model and API

[seancolsen]

Current behavior

We have a "databases" API which has developed some cruft and does not suit our changes in direction for v0.1.4.

Desired behavior

We should have a new "connections" API which behaves as follows

• Use the endpoint /api/db/v0/connections/
• Have a "nickname" field that can be changed. Nicknames must be unique across all connections within one Mathesar installation.
• Not have deleted or editable fields, as in the current "databases" API.
• Write and read connections only to and from the internal (Django) database. (This is in contrast to the old databases API which considered the environment variables to be a second source of truth for user database connections.)

[mathemancer]

Getting into implementing this.

@seancolsen I suggest making the following change as well: Changing the field db_name to simply database .

• db_name is the cause of a bunch of confusion in the back end.
• database is how the property of a connection is referred to in postgres (and other documentation).
• I'd want to go this direction anyway in the long run, may as well do it now if it's not a huge problem.

Normally, I'd just go for it, but I think this implies some front end work, and I know we're trying to get this done quickly. What do you think? Is it a huge hassle to change on the front end?

[seancolsen]

@mathemancer database sounds fine to me. Go for it.