python based regression test setup for auth_broker. This uses a http
mock for cplane as well as the JWKs url.
complications:
1. We cannot just use local_proxy binary, as that requires the
pg_session_jwt extension which we don't have available in the current
test suite
2. We cannot use just any old http mock for local_proxy, as auth_broker
requires http2 to local_proxy
as such, I used the h2 library to implement an echo server - copied from
the examples in the h2 docs.
