Increase our automated build timeout to 3 hours (#2061)

Our automated Cloud Builds run multiple long-running integration tests in both Python 2 and Python 3 environments.

As such, they've started taking longer than the previous timeout of 2 hours.

Author: ojarjur

tools/release/cloudbuild.yaml

@@ -187,4 +187,4 @@ images:
   - 'gcr.io/${PROJECT_ID}/datalab-preview'
   - 'gcr.io/${PROJECT_ID}/datalab-gpu-preview'
 
-timeout: '7200s'
+timeout: '10600s'