support the streamable part of Streamable HTTP

[topherbullock]

[palladius]

Note: Streamable HTTP is the "newer version" of SSE

[atesgoral]

@palladius Yeah! We only have the regular JSON-RPC (single transcational POST) part of it right now. The optional SSE part of it is in the works (see PR linked above).

[palladius]

Thanks, I'll try it super soon!