MFTF Support

[sprankhub]

It would be nice to provide an action for MFTF test execution.

I created this for Bitbucket Pipelines already (see https://www.coderblog.de/running-magento-2-tests-via-bitbucket-pipelines/ although probably a bit outdated), so happy to help with this.

The blackfire setup action is the closest I have come to setting up an M2 site via github actions that is accessible via a base url. I haven't seen many examples for github actions that use selenium based tests but also using a custom locally accessible domain and docker images.