Add support for multiple subdomains on microco.sm

This adds support for multiple subdomains. The request host is now used to construct the service endpoint for all API calls.

E.g. A request with Host: abc.microco.sm will result in https://abc.microco.sm/api/v1 being called.

Integration tests have also been moved out into a separate repository. In `tests.py` unit tests for `build_url` for constructing the service endpoint have been added, and a test verifying the service endpoint is derived from the request host has also been added.