Support Multiple Database Servers, supply db and creds via params

[MarkCupitt]

Problem

We run a Kubernetes Admin cluster that maintains a number of child clusters, each with their own postgres databases.

As we understand it, mathesar is deployed on a one -> one relationship per database.

Proposed solution

IT would be very useful to be able to select which server one wanted to connect to, opr even better, pass in the server required of a single running matheus instance, eg: via Header, querystring or whatever.

There user/password should be bale to be (optionally), we understand the security issues) be able to be included, along with a specific database to access. Obviously we could match read/only creds to a database or read/write depending on the users role

[rajatvijay]

@mathemancer @kgodey can you take a look?

[kgodey]

@MarkCupitt We already have some support for this (you can configure any number of databases to connect to Mathesar). Our existing permissions system should be able to handle users with different levels of permissions to different databases.

The main things missing are documenting how to set up multiple databases and UI to switch between databases. We're tracking this in #2006.

Do you think that covers your use case or is there anything missing?