Add multi-arch build (#15)

Author: wnagele

.github/workflows/publish.yml

@@ -16,9 +16,10 @@ jobs:
       contents: read
       packages: write
       attestations: write
-    uses: datum-cloud/actions/.github/workflows/publish-docker.yaml@v1.5.1
+    uses: datum-cloud/actions/.github/workflows/publish-docker.yaml@v1.8.1
     with:
       image-name: galactic-operator
+      platforms: "linux/amd64,linux/arm64"
     secrets: inherit
 
   publish-kustomize-bundles: