chore(engine): Add HTTP/2 transport for wire protocol

[ivkalita]

Implements HTTP/2 transport layer with FrameProtocol interface, HTTP2Listener/Conn, and JSONProtocol. Supports concurrent clients via per-connection protocol instances.

What this PR does / why we need it:

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

There are some issues I would like to fix in the follow up PRs (this PR is already big):

1. JSONProtocol - this should be replaced by a binary protocol of some kind (protobuf?). Added JSON protocol only to have e2e tests.
2. The protocol blocks on reading. E.g., if a sender is slow or sends a message only partially the reader will be blocked until the connection is closed.
3. The code is not instrumented at all.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[rfratto]

Looks like this is heading in the right direction. Once we serialize the physical plans as protobuf, I think we should also be serializing the frames as protobuf as well.

[rfratto]

Could we make this work by exposing an http.Handler, so that way we can reuse the existing HTTP server Loki exposes?