chore(lint): refactor Markdown linting to use markdownlint-cli2

This switches from `markdownlint-cli` to `markdownlint-cli2` and drops
usage of the https://github.com/avto-dev/markdown-lint GitHub action in CI.

- The `avto-dev/markdown-lint` action was using a 4y old version of `markdownlint`.
  AFAICT that action is not being maintained.
- There is a new `npm run lint:markdown` and the `lint.yml` CI workflow uses it.
- The switch from `markdownlint-cli` to `markdownlint-cli2` and `.markdownlint-cli2.jsonc`
  as the config allows using the https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint
  VSCode plugin for in-editor Markdown lint warnings and intellisense in the config file.

Refs: open-telemetry/opentelemetry-js#4713

.github/ISSUE_TEMPLATE/plugin_request.md

@@ -20,9 +20,11 @@ A clear and concise description of what the problem is. Ex. I'm always frustrate
 
 
 ### Do you expect this instrumentation to be commonly used?
+
 Weekly Downloads:
 
 ### What version of instrumentation are you interested in using?
+
 Versions:
 
 ### Additional context

.github/workflows/lint.yml

@@ -15,14 +15,8 @@ jobs:
         with:
           node-version: 18
           cache: 'npm'
-
-      - name: Lint markdown files
-        uses: avto-dev/markdown-lint@v1
-        with:
-          config: '.github/markdown-lint.yml'
-          ignore: "./**/CHANGELOG.md"
-          args: "./**/*.md"
-
       - run: npm ci
       - name: Lint
-        run: npm run lint
+        run: |
+          npm run lint
+          npm run lint:markdown

.markdownlint-cli2.jsonc

@@ -0,0 +1,17 @@
+// https://github.com/DavidAnson/markdownlint-cli2#markdownlint-cli2jsonc
+{
+  "config": {
+    // https://github.com/DavidAnson/markdownlint/blob/main/README.md#rules--aliases
+    "MD013": false,
+    "MD024": false,
+    "MD033": false,
+    "MD041": false,
+    "MD012": false, // no-multiple-blanks, common in CHANGELOG.md files
+    "MD045": false, // XXX no-alt-text
+    "MD026": false, // XXX drop?
+    // "MD004": { "style": "dash" } // ul-style
+  },
+  "gitignore": true,
+  "noBanner": true,
+  "noProgress": true
+}