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)

buildimages/k3d-helm/Dockerfile

+ARG DOCKER_VERSION=latest
+
+FROM docker:${DOCKER_VERSION}
+
+ARG KUBECTL_VERSION=v1.21.3
+
+RUN apk add -U wget bash openssl
+# install kubectl
+RUN wget -q -O /usr/local/bin/kubectl https://storage.googleapis.com/kubernetes-release/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl && \
+    chmod +x /usr/local/bin/kubectl
+RUN echo https://storage.googleapis.com/kubernetes-release/release/${KUBECTL_VERSION}
+# install k3d
+RUN wget -q -O - https://raw.githubusercontent.com/rancher/k3d/main/install.sh | bash
+# install Helm
+RUN wget -q -O - https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3 | bash