Allow overriding platforms to build for

Author: cbrevik

.github/workflows/cluster-docker-build-tag-push.yaml

@@ -45,6 +45,10 @@ on:
         type: string
         description: "Docker image repository name in GAR: amp = images hosted in cluster; dev = dev env and test images"
         default: amp
+      image_platforms
+        type: string
+        description: "Platform to build the image for, comma separated list. Example: linux/amd64,linux/arm64"
+        default: linux/amd64
       workload_identity_provider:
         type: string
         description: "Workload identity federation provider"
@@ -168,3 +172,4 @@ jobs:
           tags: ${{ steps.meta.outputs.tags }}
           cache-from: type=gha,scope=${{ inputs.image }}
           cache-to: type=gha,mode=max,scope=${{ inputs.image }}
+          platforms: ${{ inputs.image_platforms }}