Function to handle renaming schemas

[kgodey]

Problem

Users might want to rename schemas. We don't currently support this.

Proposed solution

A function that handles renaming of schemas in the database, including renaming references to them (foreign keys), etc.

Additional context

This should be in the db module.

[mathemancer]

We'll need to also touch the mathesar module, since we'll want to also change the name in the models for consistency.

edit: just saw #166