Wire up Authentication and Firebase

[arniber21]

This is a big task. We need to get Firebase w/ Spring Security (for authentication) and Firebase w/ Spring JPA (for database) wired up. This is gonna be really annoying and require a lot of wiring. But on the bright side, once we have this done, it's gonna be really nice to be able to ignore all Firebase complexities and pretend we're writing a regular Spring backend with all its handholding.

[arniber21]

Step 1. Install Firebase and get it set up (in progress)

• so far, Firebase configuration seems to work. We haven't tested the database yet. That is a good sign.
• We need to build the auth endpoints and get that wired up (oh boy will that be difficult).