This diff introduces a function to build a Tonic client for further API calls in integrational tests. The pointer to the client will be passed to the helper functions (in D5931) instead of making the "global" client instance.
We are using `COMM_SERVICES_TUNNELBROKER_PORT` environment variable to provide a port to connect to the Tunnelbroker.
The `COMM_SERVICES_TUNNELBROKER_HOST` environment variable provides a host to connect to the Tunnelbroker.
Linear task: [[ https://linear.app/comm/issue/ENG-1657 | ENG-1657 ]]