feat: add GH action markdown linting

* specification file

.github/workflows/validate-markdown.yaml

@@ -1,10 +1,9 @@
 name: validate-markdown
 
-# Author: @MikeRalphson
-# Issue: https://github.com/OAI/OpenAPI-Specification/issues/2130
+# Author: @ralfhandl based on work of @MikeRalphson
 
 #
-# This workflow validates files in the versions directory matching 1.*.md
+# This workflow validates markdown files in the `versions` directory matching *.md
 #
 
 # run this on push to any branch and creation of pull-requests
@@ -16,9 +15,16 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2 # checkout repo content
-    - uses: actions/setup-node@v1 # setup Node.js
+    - uses: actions/checkout@v4 # checkout repo content
       with:
-        node-version: '18.x'
+        fetch-depth: 0
+    # - name: use the javascript environment from main
+    #   run: |
+    #     git checkout remotes/origin/main -- package.json package-lock.json .markdownlint.yaml
+    - uses: actions/setup-node@v4 # setup Node.js
+      with:
+        node-version: '20.x'
     - name: Validate markdown
-      run: npx mdv versions/1.*.md
+      run: npx --yes mdv ./versions/[1-2].*.md
+    - name: Lint markdown
+      run: npx --yes markdownlint-cli --config .markdownlint.yaml versions/1.0.[^0].md versions/1.[1-9].*.md versions/2.*.md

.markdownlint.yaml

@@ -0,0 +1,12 @@
+# Unordered list indentation
+MD007:
+  indent: 2
+
+MD012: false # allow blank lines
+
+MD013:
+  line_length: 800
+  tables: false
+
+MD024: false # duplicate headings
+MD033: false # inline HTML