Switch to using GitHub action to verify markdown links for PRs (#17281)

.github/workflows/markdown-link/config.json

@@ -0,0 +1,3 @@
+{
+  "aliveStatusCodes": [504, 503, 403, 200]
+}

.github/workflows/markdownLink.yml

@@ -0,0 +1,20 @@
+on:
+  pull_request:
+    branches:
+      - master
+      - 'release/**'
+    paths:
+      - '**.md'
+
+name: Check links for modified files
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1
+      with:
+        use-quiet-mode: 'yes'
+        use-verbose-mode: 'yes'
+        check-modified-files-only: 'yes'
+        config-file: .github/workflows/markdown-link/config.json