Support new fediverse:creator notation

[SISheogorath]

Mastodon introduced some new metadata for fediverse accounts, that allow highlighting of the author in posts: https://blog.joinmastodon.org/2024/07/highlighting-journalism-on-mastodon/

With Mastodon 4.3.x rolling out to the public, it would be nice to support this as part of jekyll-seo.

The notation is rather easy:

<meta name="fediverse:creator" content="@[email protected]" />

I would suggestion to introduce a similar notation as for the twitter and facebook specific tags:

fediverse:
  username: @[email protected]

Alternatively, one could consider re-using the social section.