Run multihost tests on testing farm

[engelmi]

Please describe what you would like to see

In #662 we added multihost support for the integration tests. It would be good to provide means to run (trigger) the tests in a multihost setup on testing farm via GitHub Action. Triggering this workflow should be limited to the project committers (which should be by default) and, as a first step, manually starting them would suffice.

Note: Currently, multihost is only supported for Red Hat Ranch (see https://docs.testing-farm.io/Testing%20Farm/0.1/test-request.html#_current_limitations)

[Yarboa]

@engelmi is there future option to run it on TestingFarm public ranch?

[engelmi]

@engelmi is there future option to run it on TestingFarm public ranch?

It is not supported on Public Ranch according to testing farm limitations. As soon as this limitation isn't valid anymore, we can run them on public ranch as well.