Run nightly tests to have a chance detecting flakiness

[invidian]

Expected Behaviour

Every day e2e tests runs to ensure everything is functioning as expected.

Current Behaviour

Currently, some users may hit things like tinkerbell/osie#183, which does not happen all the time.

Possible Solution

Configure GitHub Action to run every night, so build fails are reported via email.

[tstromberg]

Seems reasonable. My concern here is that folks will just ignore the flake e-mails. The next extension from here is automatic issue opening.

[jacobweinstock]

Unfortunately at the moment manual testing is all that @chrisdoherty4 and I are able to provide. A roadmap item has been opened for discussion and community help. tinkerbell/roadmap#32