Per change request, updating registry login to utilize username from secret, instead of github running actor

.github/workflows/docker.yml

@@ -37,7 +37,7 @@ jobs:
         uses: docker/login-action@v1
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ github.actor }}
+          username: ${{ secrets.SERVICE_USER }} # Defined in secrets for auth to registry
           password: ${{ secrets.GITHUB_TOKEN }}
       - name: build and push
         uses: docker/build-push-action@v2