Create library and dockerfile for ucam-faas

Part of: https://gitlab.developers.cam.ac.uk/uis/devops/iam/idhub/api/-/issues/101

Adds python library which wraps and builds upon the google functions-framework library to provide a basic FaaS support library, including additional extensions like structlog configuration.

Adds a Dockerfile which can be used to run FaaS applications.

Test Coverage Note

Test coverage is currently low for this library. This is because a large number of lines of code go into configuring logging, which is not usefully testable (I could write a unit test that verifies that the function has been called, but ultimately I don't think that's worthwhile). While I'm happy to hear unit test comments, I'm averse to adding junk tests just to bump the coverage percentage up.