fork `activitypub-federation-rust`

[kwaa]

Due to the need to upgrade to Axum 0.7, Hatsu must maintain its own activitypub-federation-rust fork. (https://github.com/LemmyNet/activitypub-federation-rust/issues/87)

The modifications desired are as follows:

• Drop actix-web support, upgraded to axum 0.7 and hyper/http 1.0.
• Use rsa instead of openssl (https://github.com/LemmyNet/activitypub-federation-rust/pull/116)
• Use AFIT instead of async-trait (PR to upstream where possible)

[kwaa]

https://github.com/importantimport/activitypub-federation-rust

Since I don't plan on publishing to crates.io, Hatsu should use this fork as a git submodule.