Add a scheduled CI job that checks for broken or outdated links (link rot) in this repository and the lima-vm.io website.

Instead of running this as part of the PR checks (which could be noisy or slow), the job could run once a day on a schedule. This would help us detect:

• Dead or redirected links in code files
• Broken links on the website (including external references)

Originally posted by @jandubois in #3633 (review)