manpages: Convert links from http to https when valid

[bcr]

Summary

Many of our man pages contain links to websites that are still using
http. Convert them to use https. I skipped those that:

• were not available anymore,
• did not provide an SSL page,
• had caused an SSL validation error,
• were not the original link anymore (i.e. aquisition)
• where the site structure had changed, causing 404s on the new site

Event: EuroBSDcon 2026