Merge branch 'mahf708/docs/markdownlinter' (PR E3SM-Project#6342)

Adds a markdown linter on new files in PRs to ensure they conform with some
linting rules (can modify these later if needed).

[BFB]

.github/workflows/e3sm-gh-md-linter.yml

@@ -0,0 +1,28 @@
+name: markdown
+
+# if .md files are touched in a PR, lint them!
+
+on:
+  pull_request:
+    branches: ["master"]
+    paths:
+        - '**/*.md'
+
+jobs:
+  linter:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    - uses: tj-actions/changed-files@v44
+      id: changed-files
+      with:
+        files: '**/*.md'
+        separator: ","
+    - uses: DavidAnson/markdownlint-cli2-action@v16
+      if: steps.changed-files.outputs.any_changed == 'true'
+      with:
+        config: 'docs/.markdownlint.json'
+        globs: ${{ steps.changed-files.outputs.all_changed_files }}
+        separator: ","

docs/.markdownlint.json

@@ -0,0 +1,3 @@
+{
+    "line-length": false
+}