Support custom branding in Mathesar

[zackkrida]

Problem

Users have requested the ability to add a custom logo to the login page and header of Mathesar, so they can present users their own branding. This can help a Mathesar instance feel more "official" and easier to understand for non-technical users.

Proposed solution

Add the ability to include a custom logo in the Mathesar configuration. When a custom logo file is present, it should:

• Replace the Mathesar logo on the login page
• Replace the Mathesar logo in the app header
• Enable a "Powered by Mathesar" tagline elsewhere on the site, like a footer or other persistent location

Additional context

[NormannLaw]

We are a group of students from a grad-school level Open Source Software class. Can we have a chance to try working on this issue?