Setup GitHub Actions for auto remove trailing whitespaces (#4269)

* Setup GitHub Actions for auto remove trailing whitespaces

This PR setup GitHub Actions for auto remove trailing whitespaces,
if any non-go files are touched (.git directory are ignored)

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove TestTrailingWhitespace in presubmit tests

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* paths and paths-ignore are mutually exlcusive so only keep paths-ignore

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove redundent bufio import

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

.github/workflows/whitespace.yml

@@ -0,0 +1,36 @@
+name: Remove Trailing Whitespaces
+
+on:
+  push:
+    branches:
+      - 'master'
+    paths-ignore:
+      - '**.go'
+
+jobs:
+  fix:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Remove Trailing Whitespaces
+        run: |
+          find . -not -path '*/\.git/*' -type f -not -name '*.go' -exec sed -i '' 's/[[:space:]]\{1,\}$//' {} \+
+      -
+        name: Set up Git
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          git config user.name "coredns-auto-trailing-whitespaces[bot]"
+          git config user.email "coredns-auto-trailing-whitespaces[bot]@users.noreply.github.com"
+          git remote set-url origin https://x-access-token:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git
+      -
+        name: Commit and push changes
+        run: |
+          git add .
+          if output=$(git status --porcelain) && [ ! -z "$output" ]; then
+            git commit -m 'auto remove trailing whitespaces'
+            git push
+          fi