Migrate GitHub workflows to prow jobs

[ivanvc]

This was discussed during the community meeting and in #17 (comment).

Move the workflows to the prow infrastructure, and then delete the workflows from the repository.

[ivanvc]

/assign

[ivanvc]

@jmhbnz, do we want to enable /ok-to-test, here, too? It would be a good idea (and a good first issue).

[jmhbnz]

@jmhbnz, do we want to enable /ok-to-test, here, too? It would be a good idea (and a good first issue).

Yes I think we should enable same suite of plugins we use on other etcd repositories, we can do it as a separate good first issue certainly 🙏🏻