Replaces per-build on-demand installs (apk add bash/python3/curl,
curl-downloading yq to /tmp) in runHooks.groovy, syncArgoApp.groovy,
and updateHelmTag.groovy with a single custom image
(build-tools.Dockerfile) that has all of it baked in once, at
image-build time — not repeated on every single pipeline run.
updateHelmTag.groovy also now runs inside container('docker-cli')
(previously unwrapped, defaulting to the auto-injected jnlp agent
container, which is why it needed the curl-downloaded yq fallback in
the first place — that container has git but not yq).
dind-pod.yaml's docker-cli container now points at
harbor.192.168.1.7.nip.io/homelab/build-tools:1 instead of the stock
docker:27-cli — this image needs building and pushing once before any
build using this pod template will work; see build-tools.Dockerfile's
header comment.
