Consider Axum instead of Actix-Web

[joepio]

When I started with this project, actix-web was by far the most powerful and versitile web framework for rust. But it's been a couple of years, and things have changed. The tokio team have created Axum, which has a couple of advantages over Actix-Web:

• Actively maintained by the creators
• More readable documentation / easier to understand abstractions
• Seems to support sub-domains (useful for multi-tenant stuff Multi-tenancy #288)

But there's also a couple of things I need to find out, before switching:

• File upload / download. Multipart support is there.
• Static files such as the js assets, preferably compiles into the binary. Seems to be there. Can also be done with tower servedir
• Websockets. Yep, with

[AlexMikhalev]

I am fond of Poem - it can do everything the above.