[services] Tunnelbroker - Moving the config file to the ~/.config directory and removing the sandbox config

Summary:
Moving the config file for Tunnelbroker to the ~/.config directory to unify services configuration. Removing using the "sandbox" config file. Updating services documentation about the new path and removing the sandbox config.

Linear task and full context: ENG-1680

Test Plan:

1. Tunnelbroker service is successfully built.
2. Config file is successfully read from the new path.

Reviewers: jon, varun, bartek, tomek, ashoat, O6 Docs

Reviewed By: jon, varun, bartek, tomek, ashoat, O6 Docs

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5790