chore(java): enable generated-files-bot (googleapis#292)

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Synth log will be available here:
https://source.cloud.google.com/results/invocations/66e56305-8452-4efe-8c5f-b97f39f7188b/targets

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Source-Link: googleapis/synthtool@b19b401

java-resourcemanager/.github/generated-files-bot.yml

@@ -0,0 +1,7 @@
+externalManifests:
+- type: json
+  file: 'synth.metadata'
+  jsonpath: '$.generatedFiles[*]'
+- type: json
+  file: '.github/readme/synth.metadata/synth.metadata'
+  jsonpath: '$.generatedFiles[*]'

java-resourcemanager/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-resourcemanager.git",
-        "sha": "d0df733670db2d5a56cf5960bfde90a519d05e52"
+        "sha": "b9d7a5b1e4e31fcb42823a92dafbf5cd7efca606"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "f68649c5f26bcff6817c6d21e90dac0fc71fef8e"
+        "sha": "b19b401571e77192f8dd38eab5fb2300a0de9324"
       }
     }
   ],
@@ -21,6 +21,7 @@
     ".github/ISSUE_TEMPLATE/feature_request.md",
     ".github/ISSUE_TEMPLATE/support_request.md",
     ".github/PULL_REQUEST_TEMPLATE.md",
+    ".github/generated-files-bot.yml",
     ".github/readme/synth.py",
     ".github/release-please.yml",
     ".github/snippet-bot.yml",