Add lychee-based link checker

Author: Andy4495

.github/workflows/check-links.yml

@@ -0,0 +1,74 @@
+# https://github.com/lycheeverse/lychee-action
+# https://github.com/lycheeverse/lychee
+name: Check Links
+
+on:
+  push:
+  schedule:
+    # Run monthly 
+    # GitHub actions uses UTC for time zone
+    # crontab format: minute hour day-of-month month day-of-week
+    - cron: "18 4 4 * *"
+  workflow_dispatch:
+    inputs:
+      message:
+        description: Message to display in job summary
+        required: false
+        type: string
+  workflow_call:
+    inputs:
+      message:
+        description: Message to display in job summary
+        required: false
+        type: string
+      verbose:
+        description: verbosity level 
+        required: false
+        type: string
+        default: -v
+      progress-bar:
+        description: display progress bar
+        required: false
+        type: string
+        default: --no-progress
+      valid-codes:
+        description: valid http return status codes
+        required: false
+        type: string
+        default: -a '200,403,429,500'
+      base-directory:
+        description: root directory to check relative URLs
+        required: false
+        type: string
+        default: .
+      fail-mode:
+        description: true=fail action on failed check
+        type: boolean
+        default: true
+      additional-args:
+        description: Additional command-line arguments (see https://github.com/lycheeverse/lychee#commandline-parameters)
+        required: false
+        type: string
+      input-files:
+        description: Files to check links in
+        required: false
+        type: string
+        default: ./**/*.md
+
+jobs:
+  link-checker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Link Checker
+        id: lychee
+        uses: lycheeverse/lychee-action@v1
+        with:
+          # args: --base . --verbose --no-progress -a '200,403,429,500' './**/*.md' 
+          # args: --config ./.github/workflows/lychee.toml './**/*.md'
+          args: ${{ inputs.verbose }} ${{ inputs.progress-bar }} ${{ inputs.valid-codes }} ${{ inputs.base-directory }} ${{ inputs.fail-mode }} ${{inputs.additional-args }} ${{ inputs.input-files }}
+          fail: ${{ inputs.message }}
+      - name: Print the job summary
+        if: ${{ inputs.message }}
+        run: |
+          echo ${{ inputs.message }} >$GITHUB_STEP_SUMMARY