Test Helm chart in CI pipeline

Open points:

• Basic k3d cluster setup
• Move all installation etc. to dedicated builder image

Postponed to later MR:

• Use custom builder image (!283 (merged))
• Create test for running a simple benchmark (unsure if this should be done via helm test as the test pod/job would need a service account etc.), related to #202 (closed) (!285 (merged))
• Add need for deploy-theodolite (#389)