New test that checks markdown links for issues (#5924)

* New test for checking markdown links for issues

* Fix reference to test script

* Changed docs/guides/_index.md from toml to yaml

* Intentional mistake

* Additional logic for dealing with files, commands, indented code blocks, and inline code blocks

* Ignore text within the output shortcode

* Renamed test

* Fix most issues with links

* Test to check slug mismatches

* Test links script can optionally attempt to fix some issues. Update internal links script now replaces more old links

* Clean up output

.github/workflows/test.yaml

@@ -77,6 +77,23 @@ jobs:
       env:
         GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
 
+  check-links:
+    name: Check Links (Markdown)
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v3
+      with:
+        python-version: '3.11.x'
+        architecture: 'x64'
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install python-frontmatter
+    - name: Run tests
+      run: python ./ci/check-links.py ${{ steps.files.outputs.all }}
+
   docs404:
     runs-on: ubuntu-latest
     steps: