Add CI E2E testing for k8s-cluster-api-provider project

Created by: matofeder

This PR adds the following:

• .zuul.yaml configuration file that informs Zuul about the project's CI settings, pipelines and jobs
• pipelines:
  • e2e-test that executes k8s-cluster-api-provider-e2e-conformance job
  • unlabel-on-update-e2e-test that ensures that any PR update invalidates a previous successful e2e test
  • e2e-quick-test that executes k8s-cluster-api-provider-e2e-quick job
  • unlabel-on-update-e2e-quick-test that ensures that any PR update invalidates a previous successful e2e test
• jobs:
  • k8s-cluster-api-provider-e2e-conformance that runs a sonobuoy conformance test against Kubernetes cluster spawned by k8s-cluster-api-provider scripts
  • k8s-cluster-api-provider-e2e-quick that runs a sonobuoy quick test against Kubernetes cluster spawned by k8s-cluster-api-provider scripts
• docs

read the docs for further details

Note1: This PR depends on zuul-config PRs:

• https://github.com/SovereignCloudStack/zuul-config/pull/21 (must have)
• https://github.com/SovereignCloudStack/zuul-config/pull/24 (optional - some fine-tune of pipelines)

Note2: This PR can not be tested by e2e-test nor e2e-quick-test as the SCS Zuul instance seems to be still under maintenance

Closes: https://github.com/SovereignCloudStack/issues/issues/408 https://github.com/SovereignCloudStack/issues/issues/382 https://github.com/SovereignCloudStack/issues/issues/407