build: add attestation for docker image

Author: wiltort

.github/workflows/build.yml

@@ -38,6 +38,13 @@ jobs:
         push: true
         tags: ${{ steps.meta.outputs.tags }}
         labels: ${{ steps.meta.outputs.labels }}
+    
+    - name: Generate artifact attestation
+      uses: actions/attest-build-provenance@v3
+      with:
+        subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
+        subject-digest: ${{ steps.push.outputs.digest }}
+        push-to-registry: true
 
     - name: Deploy to VPS
       uses: appleboy/ssh-action@master