Implement MongoDB database adapter (#29)

* Implement MongoDB adapter using motor

* Add mongo container to build pipeline

* Tidy up dependencies

* Update documentation for MongoDB

* Export MongoDB adapter from db package

* Pass black format

* Update README

docs/src/full_mongodb.py

@@ -0,0 +1,37 @@
+import motor.motor_asyncio
+from fastapi import FastAPI
+from fastapi_users import BaseUser, FastAPIUsers
+from fastapi_users.authentication import JWTAuthentication
+from fastapi_users.db import MongoDBUserDatabase
+
+DATABASE_URL = "mongodb://localhost:27017"
+SECRET = "SECRET"
+
+
+client = motor.motor_asyncio.AsyncIOMotorClient(DATABASE_URL)
+db = client["database_name"]
+collection = db["users"]
+
+
+user_db = MongoDBUserDatabase(collection)
+
+
+class User(BaseUser):
+    pass
+
+
+auth = JWTAuthentication(secret=SECRET, lifetime_seconds=3600)
+
+app = FastAPI()
+fastapi_users = FastAPIUsers(user_db, auth, User, SECRET)
+app.include_router(fastapi_users.router, prefix="/users", tags=["users"])
+
+
+@fastapi_users.on_after_register()
+def on_after_register(user: User):
+    print(f"User {user.id} has registered.")
+
+
+@fastapi_users.on_after_forgot_password()
+def on_after_forgot_password(user: User, token: str):
+    print(f"User {user.id} has forgot their password. Reset token: {token}")