Basic end-to-end test framework

[auhlig]

Umbrella issue for tracking e2e test framework efforts.
Granular sub-issues can be found via label WP2.3.4.6 End-to-end test framwork.

Greenhouse should have an e2e test framework to ensure the stability and reliability of our platform.

1. Define test framework feat(test): creating local cluster for e2e  #250 Feat(e2e): test setup #276
2. Define test scenarios End-to-end test scenarios #12 [FEAT] - E2E Plugin Lifecycle #419
3. Define test setup. Should run locally + in PR as well.
4. Define integration in CI [FEAT] - E2E Workflow #467
5. Documentation

Acceptance criteria:

• E2E tests are implemented and cover the identified critical scenarios.
• E2E tests run successfully on the CI/CD pipeline.
• Documentation for running E2E tests is provided.
• Metrics, alerts and visualization integration. Showcasing stability + trend

[uwe-mayer]

Define test scenarios here: #12

[uwe-mayer]

Update:

• We can direct e2e tests to be executed against remote greenhouse clusters with minor changes to our existing test setup and by using the USE_EXISTING_CLUSTER
• We need a way to start up a local kind cluster with a greenhouse installation. Preferably from go code, so we do not have dependency to kind on the host. But that is still up for discussion. In the end we would like to have a Make target e.g. make e2e-local that spins up the greenhouse kind cluster and points the e2e setup to execute against it, by simply exposing a KUBECONFIG env var.

[auhlig]

see #211