Add workflow using lychee to ensure that links in documentation files resolve

.github/workflows/link-checker.yml

@@ -0,0 +1,21 @@
+name: Link Checker
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  linkchecker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: lychee Link Checker
+        id: lychee
+        uses: lycheeverse/lychee-action@master
+        with:
+          args: --accept=200,403,429  **/*.html **/*.md **/*.txt **/*.json --exclude-path src/test/resources/dlsfls/logs_bulk_data.json
+        env:
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      - name: Fail if there were link errors
+        run: exit ${{ steps.lychee.outputs.exit_code }}

.lycheeignore

@@ -0,0 +1,4 @@
+http://localhost:9200/
+http://localhost:33667/
+http://test.entity/
+https://github.com/opendistro-for-elasticsearch/security/