ci: Add link checking to CI (#6168)

Rather than integrate the docs tool, this uses
https://github.com/lycheeverse/lychee-action?tab=readme-ov-file.

It will file a ticket if there are broken links. If that's not the best
way, it can be made to notify Slack instead.

.github/workflows/links.yml

@@ -0,0 +1,25 @@
+name: Links
+
+on:
+  repository_dispatch:
+  workflow_dispatch:
+  schedule:
+    - cron: "00 18 * * *"
+
+jobs:
+  linkChecker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Link Checker
+        id: lychee
+        uses: lycheeverse/lychee-action@v2
+
+      - name: Create Issue From File
+        if: env.lychee_exit_code != 0
+        uses: peter-evans/create-issue-from-file@v5
+        with:
+          title: Link Checker Report
+          content-filepath: ./lychee/out.md
+          labels: report, automated issue