Add docker syntax directive and a validation check

Author: lfrancke

.github/workflows/pr_pre-commit.yml

@@ -18,6 +18,8 @@ jobs:
         with:
           python-version: '3.12'
       - name: Setup Hadolint
+        # We need to download this here due to a bug in the pre-commit/hadolint setup
+        # https://github.com/hadolint/hadolint/issues/886
         shell: bash
         run: |
           set -euo pipefail

template/docker/Dockerfile.j2

@@ -1,7 +1,11 @@
+# syntax=docker/dockerfile:1.10.0@sha256:865e5dd094beca432e8c0a1d5e1c465db5f998dca4e439981029b3b81fb39ed5
 # =============
 # This file is automatically generated from the templates in stackabletech/operator-templating
 # DON'T MANUALLY EDIT THIS FILE
 # =============
+# NOTE: The syntax directive needs to be the first line in a Dockerfile
+# https://docs.docker.com/build/checks/#fail-build-on-check-violations
+# check=error=true
 FROM oci.stackable.tech/sdp/ubi9-rust-builder AS builder
 
 FROM registry.access.redhat.com/ubi9/ubi-minimal AS operator