fix: don't allow FQDN links

[nschonni]

Adds another Markdownlint Search/Replace rule to prevent https://developer.mozilla.org links, since they should be absolute links instead.
Because the root Markdownfiles actually need the FQDN links, I swapped them to use Reference links so the regex doesn't catch them. Easier way would be a trailing Markdownlint disable comment, but those haven't been accepted in the past for other PRs, so this is the workaround

[github-actions]

Preview URLs

• /en-US/docs/MDN/Community/Pull_requests
• /en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license
• /en-US/docs/Web/HTML/Element/video

Flaws (2)

Note! 1 document with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/MDN/Community/Pull_requests
Title: Pull request guidelines
Flaw count: 1

• broken_links:
  • Anchor not lowercase

---

URL: /en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license
Title: Attribution and copyright licensing
Flaw count: 1

• broken_links:
  • Link points to the page it's already on

(this comment was updated 2022-11-11 11:06:47.137740)

[bsmth]

Opening as a draft, because there are still some links in the meta/ site that are pending deletion in another PR

This is now complete:

• Remove meta site #20775

[bsmth]

Thanks @nschonni, I think we can merge this one 👍🏻

[bsmth]

Merging shortly