Move CA set up from SSLAuthenticationTest into re-usable util

This will become a new module that different test suites can depend upon.

This will not be public API as it is a test suite utility but we will still want to be cautious of any API changes as these will cause problems for dependent projects.

Additionally this is intended as a common CA set up used across tests but different tests may have different requirements so any API should allow customisation / filtering of the relevant artefacts produced.