feat!: Replace markdownlint with prettier

We use prettier in 95% of our repos for formatting markdown. This
codifies/automates that choice.

Author: lihu

.github/workflows/markdownlint.yaml

@@ -0,0 +1,53 @@
+---
+"on":
+  workflow_call:
+    inputs:
+      jobs_run_on:
+        default: "ubuntu-latest"
+        description: "The runner group on which jobs will run."
+        required: false
+        type: "string"
+      timeout_minutes:
+        description: "The maximum time (in minutes) for a job to run."
+        default: 5
+        required: false
+        type: "number"
+      working_directory:
+        description: "The working directory where all jobs should be executed."
+        default: "."
+        required: false
+        type: "string"
+jobs:
+  prettier:
+    defaults:
+      run:
+        working-directory: "${{ inputs.working_directory }}"
+    runs-on: "${{ inputs.jobs_run_on }}"
+    timeout-minutes: "${{ inputs.timeout_minutes }}"
+    env:
+      PRETTIER_VERSION: "3"
+    steps:
+      - name: "Checkout repo"
+        uses: "actions/checkout@v4"
+      - name: "Set up Node.js"
+        uses: "actions/setup-node@v4"
+        with:
+          node-version: "22.x"
+      - name: "Get yarn cache directory"
+        id: "cache-dir"
+        run: >-
+          echo "dir=$(yarn cache dir)" >> $GITHUB_OUTPUT
+      - uses: "actions/cache@v4"
+        id: "cache"
+        with:
+          path: "${{ steps.cache-dir.outputs.dir }}"
+          key: "${{ runner.os }}-prettier@${{ env.PRETTIER_VERSION }}"
+      - name: "Install prettier"
+        run: >-
+          yarn add "prettier@${{ env.PRETTIER_VERSION }}"
+      - name: "Put node executables in the system PATH"
+        run: >-
+          echo -n "$(yarn bin)" >> $GITHUB_PATH
+      - name: "Check all files with prettier"
+        run: >-
+          prettier --prose-wrap always --check **/*.md

.github/workflows/prettier.yaml

@@ -113,25 +113,17 @@ and the [release-please-action](https://github.com/googleapis/release-please-act
 These are local Actions that run for this repository. This workflow is not
 visible or usable outside of this repository.
 
-### markdownlint.yaml
-
-This workflow will run the
-[DavidAnson/markdownlint-cli2-action](https://github.com/DavidAnson/markdownlint-cli2-action)
-action to lint markdown files.
-
-#### markdownlint Inputs
-
-* `config_file`: The configuration file to use. Default: `.markdownlint-cli2.yaml`
-* `fix`: If set to true, fix any issues found. Default: `false`
-* `globs`: The glob to use to find all markdown files. Default: `**/*.md`
-* `separator`: The character used to separate globs. Default: `,`
-
 ### pre-commit.yaml
 
 This workflow runs the
 [pre-commmit action](https://github.com/pre-commit/action) with minimal options
 for configuration.
 
+### prettier.yaml
+
+This workflow will run [prettier](https://prettier.io/) to check formatting of
+markdown files. The only option passed is `--prose-wrap always`.
+
 ### puppet-build.yaml
 
 This workflow will setup [Puppet][7] using