Add testing on OpenShift 4

Right now we have a public AMI which runs OpenShift 3.11 using oc cluster up. The code for this is in ods-devenv.

We need to have E2E tests for ODS on OpenShift 4 as well. The question is how we want to achieve this.

OpenShift 4 does not have oc cluster up anymore. Instead, https://github.com/code-ready/crc should be used. Unfortunately, the standard crc needs an image pull secret, which is personal and therefore cannot be shared.

Since a few weeks, there is an OKD variant of crc available at https://www.okd.io/crc.html, which does not need the image pull secret. However, there might be (significant) differences to an actual OpenShift installation.

Further, I tried to run the OKD variant of crc in GitHub Actions in https://github.com/michaelsauter/crc-okd-action-test/runs/1478942209?check_suite_focus=true, which fails due to not enough memory:

CodeReady Containers version: 1.19.0-OKD+deb39a0
OpenShift version: 4.5.0-0.okd-2020-10-15-235428 (embedded in executable)
...
crc requires at least 9.664GB to run
Error: Process completed with exit code 1.

FYI @clemensutschig @metmajer @georgfedermann