Move doc test to workflow (#3800)

Replace doc CI test with automatic workflow.

Signed-off-by: Ben Kochie <superq@gmail.com>

.github/fixup_file_mtime.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+#
+# Description: Fix up the file mtimes based on the git log.
+
+set -u -o pipefail
+
+if [[ ! -f 'coredns.1.md' ]]; then
+  echo 'ERROR: Must be run from the top of the git repo.'
+  exit 1
+fi
+
+for file in coredns.1.md corefile.5.md plugin/*/README.md; do
+  time=$(git log --pretty=format:%cd -n 1 --date='format:%Y%m%d%H%M.%S' "${file}")
+  touch -m -t "${time}" "${file}"
+done

.github/workflows/make.doc.yml

@@ -0,0 +1,45 @@
+name: make doc
+
+on:
+  push:
+    branches:
+      - 'master'
+    paths:
+      - '.github/workflows/make.doc.yml'
+      - 'coredns.1.md'
+      - 'corefile.5.md'
+      - 'plugin/*/README.md'
+
+jobs:
+  fix:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Setup Go
+        uses: actions/setup-go@v2-beta
+        with:
+          go-version: '^1.14.1'
+      -
+        name: Update Docs
+        run: |
+          ./.github/fixup_file_mtime.sh
+          make -f Makefile.doc
+      -
+        name: Set up Git
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          git config user.name "coredns-auto-go-mod-tidy[bot]"
+          git config user.email "coredns-auto-go-mod-tidy[bot]@users.noreply.github.com"
+          git remote set-url origin https://x-access-token:${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 make -f Makefile.doc'
+            git push
+          fi