Allow specifying client-id with docker-compose

[djmitche]

#62 added support for a client-id allowlist, and #53 makes it super-easy to run the server for a single-user configuration. Let's put those two together and make it possible to limit that single-user configuration to a single client-id, so users don't get taken advantage of by people uploading versions to other clients.

Something like

TASKCHAMPION_SYNC_SERVER_CLIENT_ID=<uuid> TASKCHAMPION_SYNC_SERVER_HOSTNAME=<hostname> docker up