Create add and delete user functions

[kadenlei]

Overview

Created functions to add and delete users to/from firebase by phone number. Can also add claim (number from 0-3 specifying role) for user when adding. Also made test routes to ensure functionality.

Changes Made

Created functions createUser() and deleteUser() in backend/src/users/firebase-functions.ts. Should put service account key in the users folder.

Test Coverage

Created test routes in backend/src/users/views.ts to add and delete users from the database.