build: add generated-files bot config (#36)

This PR was generated using Autosynth. 🌈

Synth log will be available here:
https://source.cloud.google.com/results/invocations/29ddb9e6-1ff3-4c74-8153-92d341c7b0a6/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

Source-Link: googleapis/synthtool@e6f3d54
Source-Link: googleapis/synthtool@5a6f30b
Source-Link: googleapis/synthtool@c6706ee
Source-Link: googleapis/synthtool@b33b0e2
Source-Link: googleapis/synthtool@898b38a

packages/google-appengine/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-appengine-admin.git",
-        "sha": "850ef480256b956fd05bda6b85b007c50f6fd875"
+        "sha": "561d77a1be6703058858831b2f4896be936e604a"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "79c8dd7ee768292f933012d3a69a5b4676404cda"
+        "sha": "e6f3d54be015a394b6ab5a25903ec09062a2b424"
       }
     }
   ],