feat: add app protocol

[OfTheDelmer]

Why

We'd like to be able specify http2 when building an http tunnel

How

Add app_protocol to the builder and plumb the forwards_proto into the session rpc.

Validation

Run an example with the http2 app protocol and confirm the correct forwardsProto was set to "http2" or "" .

[jrobsonchase]

After looking over this, I'm less sure about the enum approach. We might want to make it a string all the way through and defer validation to our hosted services. That way we can add new protocols we support there and don't have to go and update the sdk for each one. If we took that approach, the only thing I'd do in the builder methods would be to .to_lowercase() it.

Ultimately up to product though. @salilsub thoughts?

[jrobsonchase]

Current dependencies on/for this PR:

• main
  • PR feat: add app protocol  #130 👈
    • PR ngrok: set the alpn field when app_protocol is specified #131

This stack of pull requests is managed by Graphite.

[salilsub]

I think as a general rule we should push more validation to our hosted services so we can adjust those rules over time. There will be exceptions, but I think @jrobsonchase is right on this one.