Migrate status page updates to Mastodon

[LawnGnome]

The Twitter/X/Elon-fever-dream integration on Statuspage isn't working any more for us, but we want to migrate to Mastodon anyway.

TODO:

• Provision Mastodon instance
• Set up Statuspage integration
• Replace links in page footer (and anywhere else they may appear)

[Skgland]

Should this take #9634 into account and maybe not use a .io domain?
What about using the existing social.rust-lang.org?