Http 2.0 streaming

After my last issue we realized gleam_hackney already suports http 2.0 out of the box, great and. thank you Louis! But one caveat I found is that non-finite requests responses, useful for streaming gRPC, are not supported. What do you think of adding support for opening streams, consuming, and closing them?

The issue names no files, entry points, or tests. Start by locating the existing HTTP/2 request and response-handling API, then trace how non-finite responses are represented. Done should be defined as a documented way to open, consume, and close streams for streaming gRPC responses, with coverage for that lifecycle.

Written by the indexing model from the issue text.