SSE - sever side events

[Distortedlogic]

Feature Request

server side events should be ubiquitous enough at this point to not need a bunch of reasoning n explaining from me. Didnt see any issue open yet for it, or see anything about it in the docs.

[ealmloff]

It doesn't follow the SSE format, but server functions do support streaming input and output with StreamingJson added in https://github.com/leptos-rs/leptos/pull/2623

[jkelleyrtp]

Just added in #4596