Add GH action to check links in md files (#8346)

* Add GH action to check links in md files

* remove empty line

* test

* Only check modified files

* add config file

* upate checkout version

* add base branch

* add ignore pattern

* Update markdown-link-check.yml

---------

Co-authored-by: Rich Lander <rlander@microsoft.com>

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

@@ -0,0 +1,8 @@
+{
+  "ignorePatterns": [
+    {
+      "pattern": "^http://localhost"
+    }
+  ],
+  "aliveStatusCodes": [429, 200]
+}

.github/workflows/markdown-link-check.yml

@@ -0,0 +1,16 @@
+name: Check Markdown links
+
+on: push
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - 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-check-config.json'
+        base-branch: 'main'