FAPI2 machine-to-machine conformance tests

As per https://bitbucket.org/openid/fapi/issues/752/request-for-a-tailored-fapi-20-conformance we need to develop a version of the FAPI tests that work without the (technically optional) authorization code flow part of FAPI2.

They would need to use the client credentials grant at the token endpoint to directly obtain an access token instead of the authorization code flow / authorization endpoint. This would mean that the PAR endpoint also isn't used.

We already have some code that does client credentials call as it is used as a pre-test step in Brazil & UK OpenBanking.

We'd need to take that code and do something kind of like the Brazil/UK code does (but using the scopes/rar request configured in the test config) that replaces the authorization code flow, and results in the access token from the client credentials grant being used in the subsequent tests at the resource endpoint.

We'd need to do both the RP & OP tests and setup RP-against-OP tests and should be able to set CI up against the existing Authlete server I'd hope.

I'm undecided if this should be a new test plan or another option in the current test plan.