Create link check task (#8471)

.vsts-ci/spelling.yml

@@ -30,17 +30,23 @@ phases:
       Get-ChildItem -Path env:
     displayName: Capture environment
     condition: succeededOrFailed()
-
   - bash: |
       sudo npm install -g markdown-spellcheck@0.11.0
     displayName: Install mdspell
     condition: succeededOrFailed()
-
+  - bash: |
+      sudo npm install -g markdown-link-check@3.7.2
+    # WARNING: Keep markdown-link-check pinned at 3.7.2 OR ELSE...
+    displayName: Install markdown-link-check
+    condition: succeededOrFailed()
   - powershell:  Write-Host "##vso[build.updatebuildnumber]$env:BUILD_SOURCEBRANCHNAME-$env:BUILD_SOURCEVERSION-$((get-date).ToString("yyyyMMddhhmmss"))"
     displayName: Set Build Name for Non-PR
     condition: ne(variables['Build.Reason'], 'PullRequest')
-
   - bash: |
       mdspell '**/*.md' '!**/Pester/**/*.md' --ignore-numbers --ignore-acronyms --report --en-us;
     displayName: Test Spelling
     condition: succeededOrFailed()
+  - bash: |
+      find . -name \*.md -exec markdown-link-check {} \;
+    displayName: Test Links
+    condition: succeededOrFailed()