3rd-party media hosting category updates

[sarah11918]

Description (required)

This PR updates our existing Digital Asset Management section:

• Renames the category to Image and Media Hosting.
• Updates some other references around docs (e.g. imports, images pages) to refer to hosted media services.
• Adds a new Mux guide in the category and uses them as the example for video hosting in Astro.

To-do

• Verify all external Mux links (we will need to update to Astro-specific links in their documentation once available)

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Tracked Files

File	Note
en/guides/images.mdx	Source changed, localizations will be marked as outdated.
en/guides/imports.mdx	Source changed, localizations will be marked as outdated.
en/guides/media/index.mdx	Source changed, localizations will be marked as outdated.
en/guides/media/mux.mdx	Localization added, will be marked as complete.
src/content/i18n/en.yml	Source changed, localizations will be marked as outdated.
src/content/nav/en.ts	Source changed, localizations will be marked as outdated.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[yanthomasdev]

LGTM!