What does this PR change? What problem does it solve?

In previous issues (#1189 #81 #1805) people has requested to add support for a mastodon share icon. In #1240 a user created a pull request triying to add compatibility for mastodon support but the problem with the numerous instances in the fediverse was mentioned and the pull request was closed. Recently I've found a project that solve this.

This project by @barredo@mastodon.social give us this url https://mastodonshare.com/?text=text&url=yourURL.com that will promt the user for its instance and remember it with a nice gui. The next time a user click, it will remember your instance and redirect the share information to it. More info of how this works in the about section.

This pr works on it own and no more changes are nedded. It seems that the author is an active fediverse developer and has another projects like the client Mastodeck.

Was the change discussed in an issue or in the Discussions before?

PR Checklist

• This change adds/updates translations and I have used the template present here.
• I have enabled maintainer edits for this PR.
• I have verified that the code works as described/as intended.
• This change adds a Social Icon which has a permissive license to use it.
• This change does not include any CDN resources/links.
• This change does not include any unrelated scripts such as bash and python scripts.
• This change updates the overridden internal templates from HUGO's repository.