Use custom runner image with jq, kustomize, docker pre-installed

Build a runner-image based on node:20-bookworm with all CI tools
baked in, avoiding apt-get install in every workflow run. Runner
labels now point to gitea.coreworlds.io/lazorgurl/runner-image.

infra/kubernetes/platform/gitea-runner/Dockerfile.runner-image

@@ -0,0 +1,10 @@
+FROM node:20-bookworm
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    jq \
+    curl \
+    git \
+    docker.io \
+  && curl -sL https://github.com/kubernetes-sigs/kustomize/releases/download/kustomize%2Fv5.6.0/kustomize_v5.6.0_linux_amd64.tar.gz \
+    | tar xz -C /usr/local/bin \
+  && apt-get clean && rm -rf /var/lib/apt/lists/*