hyperv, openhcl, vmm_tests: onboard vmbus relay test for TDX

[chris-oo]

We have a TDX pool available, so we should onboard a basic test that uses vmbus relay to stop future regressions.

[chris-oo]

Especially important once #1207 is in

[kmehtaintel]

Please assign this to me.

[chris-oo]

Trevor is to update the docs so that other contributors can more easily add tests.