Docker: Allow fully disabling Firebase and update Docker images build instructions

[mal1k-me]

I tried to run Monkeytype Docker Compose setup and after fixing trivial problems (like file names issues) I couldn't bypass Firebase requirements because it seems to be hardcoded even if the related env vars aren't set (i.e. commented out)

monkeytype-backend   | 29-Apr-2025 21:34:13.730 Connected to database
monkeytype-backend   | 29-Apr-2025 21:34:13.730 Initializing Firebase app instance...
monkeytype-backend   | 29-Apr-2025 21:34:13.730 Failed to boot server
monkeytype-backend   | 29-Apr-2025 21:34:13.731 Internal Server Error 1aee524e-9432-4d1c-9d2f-885d17f339cc
monkeytype-backend   | [
monkeytype-backend   | init() firebase-admin.ts] {
monkeytype-backend   |   status: 500,
monkeytype-backend   |   errorId: '1aee524e-9432-4d1c-9d2f-885d17f339cc',
monkeytype-backend   |   uid: undefined,
monkeytype-backend   |   message: 'Internal Server Error 1aee524e-9432-4d1c-9d2f-885d17f339cc'
monkeytype-backend   | }
monkeytype-mongodb   | {"t":{"$date":"2025-04-29T21:34:13.740+00:00"},"s":"I",  "c":"NETWORK",  "id":22944,   "ctx":"conn2","msg":"Connection ended","attr":{"remote":"172.18.0.4:42504","uuid":"daf56288-3d36-4482-b1e3-1cd4fcd33c46","connectionId":2,"connectionCount":0}}
Gracefully stopping... (press Ctrl+C again to force)
dependency failed to start: container monkeytype-backend is unhealthy

There should be a FIREBASE_DISABLE variable or something similar. Turning off account and profile creation ability doesn't solve it (per SELF_HOSTING.md)

"users": {
     "signUp": false,
     "profiles": {
       "enabled": false
     }

---

I modified the init function in firebase-admin.ts as a workaround and when I tried to build the images I got this

❯ docker build --progress=plain --no-cache -t monkeytype/monkeytype-backend:latest . -f  ./docker/backend/Dockerfile
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            Install the buildx component to build images with BuildKit:
            https://docs.docker.com/go/buildx/

unknown flag: --progress

Usage:  docker build [OPTIONS] PATH | URL | -

Run 'docker build --help' for more information

[yehjames]

same issue here

[fehmer]

fix: #6685