Add orka/ssh integration test

⚠ This MR is based on top of !123 (merged) ⚠

Please merge first the dependent MR, then change the target branch here to master and continue with review

Issue: #35 (closed)

Add integration test for the orka provider & ssh executor. This integration test will run a dummy build in our orka cluster and ensure it runs as expected.

This necessitates an update of our CI image, to install Openconnect since Alpine doesn't have it. I moved it to a base ubuntu image so we can manage our own dependencies and don't depend on the go image updating their own base OS (see gitlab-org/gitlab-runner#27279)