feature: Support for SSE

[B45man]

Is your feature request related to a problem? Please describe. Following this previous issue, I am using Refit v6, and am very happy with it so far. I am now running into the situation that I have to consume Server Side Events. Does Refit support this yet?

Describe the solution you'd like Support for consuming SSE's. I'll take whatever I can get, but I imagine it being a client that I can tell to start or stop, and pass a delegate to it for handling messages that come in.

Describe alternatives you've considered A different library or rolling my own solution (but I'd rather keep all my HTTP requests in one library).