fix: Correct builder scheme in Cloud Build config

Author: cdata

cloudbuild.yaml

@@ -1,5 +1,5 @@
 steps:
-- name: 'usuba:latest'
-  args: ['build', '-t', 'usuba:latest', '-f', './rust/usuba/Dockerfile', '.']
+- name: 'gcr.io/cloud-builders/docker'
+  args: ['build', '-t', 'gcr.io/$PROJECT_ID/usuba', '-f', './rust/usuba/Dockerfile', '.']
 options:
   logging: CLOUD_LOGGING_ONLY