[CI] Add Markdown links check

OpenAssetIO/OpenAssetIO#737
Validate that markdown links are valid in CI.

Signed-off-by: Elliot Morris <elliot.morris@foundry.com>

Author: elliotcmorris

.github/workflows/code-quality.yml

@@ -42,3 +42,9 @@ jobs:
 
       - name: Check Python formatting
         run: black --check .
+
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1