Investigate SSE with hyper

[paulhauner]

Description

In the Eth2 API standardisation efforts, SSE (server-side events) have been suggested to handle the seemingly necessary streaming endpoints.

AFAIK, hyper doesn't come out-of-the-box with support for SSE. That being said, a web search shows several crates purporting to provide SSE in hyper.

It would be great to know:

• Is it feasible to do SSE with our current hyper stack
• If it's feasible
  • What's the effort look like? (hours, days, weeks, etc)
  • Will it be elegant?

[adaszko]

Pick me, pick me!

[adaszko]

Done via #1107