refactor: use .env for Authelia password hash

- Rename users_database.yml to users_database.template.yml
- Use envsubst to substitute AUTHELIA_USER_PASSWORD_HASH from .env
- Update configuration.yml to use /config/users_database.yml
- Add AUTHELIA_USER_PASSWORD_HASH environment variable to compose
- Password hash now stored securely in .env instead of git

net/authelia/configuration.yml

@@ -41,7 +41,7 @@ authentication_backend:
     disable: false
   refresh_interval: 5m
   file:
-    path: /etc/authelia/users_database.yml
+    path: /config/users_database.yml
     password:
       algorithm: argon2
       argon2: