ci(java): suggest formatting fixes

GitHub action config to run the java formatter and suggest inline fixes on the pull request.

This was tested in java-asset: [example PR](googleapis/java-asset#392).

Source-Author: Jeff Ching <chingor@google.com>
Source-Date: Tue Oct 13 09:04:08 2020 -0700
Source-Repo: googleapis/synthtool
Source-Sha: b65ef07d99946d23e900ef2cc490274a16edd336
Source-Link: googleapis/synthtool@b65ef07

.github/workflows/formatting.yaml

@@ -0,0 +1,25 @@
+on:
+  pull_request_target:
+    types: [opened, synchronize]
+    branches:
+      - master
+name: format
+jobs:
+  format-code:
+    runs-on: ubuntu-latest
+    env:
+      ACCESS_TOKEN: ${{ secrets.YOSHI_CODE_BOT_TOKEN }}
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: ${{github.event.pull_request.head.ref}}
+          repository: ${{github.event.pull_request.head.repo.full_name}}
+      - uses: actions/setup-java@v1
+        with:
+          java-version: 11
+      - run: "mvn com.coveo:fmt-maven-plugin:format"
+      - uses: googleapis/code-suggester@v1.8.0
+        with:
+          command: review
+          pull_number: ${{ github.event.pull_request.number }}
+          git_dir: '.'

synth.metadata

@@ -11,7 +11,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "0762e8ee2ec21cdfc4d82020b985a104feb0453b"
+        "sha": "b65ef07d99946d23e900ef2cc490274a16edd336"
       }
     }
   ],
@@ -26,6 +26,7 @@
     ".github/trusted-contribution.yml",
     ".github/workflows/auto-release.yaml",
     ".github/workflows/ci.yaml",
+    ".github/workflows/formatting.yaml",
     ".kokoro/build.bat",
     ".kokoro/build.sh",
     ".kokoro/coerce_logs.sh",