[ci] Make repository field in image parameterized

Downstream github forks can not enable CI since the build-docker workflows is hardcoded to push to the pulp-platform organization

.github/workflows/build-docker.yml

@@ -8,6 +8,9 @@ on:
   push:
     branches: [main]
   workflow_dispatch:
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
 jobs:
   build-docker:
     name: Deploy Docker image
@@ -21,12 +24,18 @@ jobs:
           registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
       - name: Build and push
         uses: docker/build-push-action@v2
         with:
           context: .
           file: util/container/Dockerfile
           push: true
-          tags: ghcr.io/pulp-platform/snitch_cluster:${{ github.ref_name }}
+          labels: ${{ steps.meta.outputs.labels }}
+          tags: ${{ steps.meta.outputs.tags }}
           build-args: |-
             SNITCH_LLVM_VERSION=latest