Reference local favicon images

[peterbe]

What was wrong/why is this fix needed? (quick summary only)

Some pages relied on favicon images that would be part of the MDN platform. Clearly that didn't work out because MDN changed favicon images.
This PR solves that by download the images locally so the images are owned by the content and not optimistically dependent on something external.

MDN URL of the main page changed

See preview URLs

Issue number (if there is an associated issue)

Anything else that could help us review it

Based on #6001 (comment)

[peterbe]

Note, this PR also fixes 2 images (clock-demo-200px.png and clock-demo-400px.png) that incorrectly was referred to as the file attachments on mdn.mozillademos.org. So I fixed that too.

[peterbe]

@rachelandrew Sorry for the notification noise. I'm manually changing reviewer to @sideshowbarker because he worked on #6001.

[github-actions]

Preview URLs

• https://pr6052.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTML/Attributes/rel
• https://pr6052.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTML/Element/img
• https://pr6052.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTML/Element/menuitem
• https://pr6052.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTML/Element/figure

Flaws

Note! 2 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/HTML/Attributes/rel
Title: HTML attribute: rel
on GitHub
Flaw count: 1

• bad_bcd_queries:
  • No BCD data for query: html.elements.attributes.rel

---

URL: /en-US/docs/Web/HTML/Element/figure
Title: <figure>: The Figure with Optional Caption element
on GitHub
Flaw count: 2

• broken_links:
  • Can't resolve /en-US/docs/Web/Guide/HTML/Using_HTML_sections_and_outlines#sectioning_roots
  • Can't resolve /en-US/docs/Web/Guide/HTML/Using_HTML_sections_and_outlines#sectioning_roots

External URLs

URL: /en-US/docs/Web/HTML/Attributes/rel
Title: HTML attribute: rel
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTML/Element/img
Title: <img>: The Image Embed element
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTML/Element/menuitem
Title: <menuitem>
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTML/Element/figure
Title: <figure>: The Figure with Optional Caption element
on GitHub

No new external URLs