Leverage `setInterval` vs `setTimeout` for Firestore connection check

[pattishin]

Original conversation: https://github.com/GoogleCloudPlatform/developer-journey-app/pull/97/files/19346d493c193f9ff6c630de1a126929b240f49d#r1275425395

Ref: src/lib/database.ts -> isConnected()

Request to use setInterval over Promise.race and setTimeout (in src/lib/database.ts).
It seems this.db.listCollections could be polled rather than giving it a timer for Promise.race to compete against. This could also make the isConnected function a little more efficient.