Check protocol version

[slinkydeveloper]

Fix #235

[slinkydeveloper]

In case of protocol version incompatibility, this is the behavior:

• The runtime ends up in a retry loop, prints

2024-02-08T14:04:48.582810Z WARN restate_invoker_impl
  Error when executing the invocation, retrying in 10s.
    error: [RT0007] [Unknown] unknown. For more details, look at the docs with https://docs.restate.dev/references/errors#RT0007
    restate.error.code: RT0007
    restate.invocation.id: inv_12LP4netCRaH6DrniM3ENA32Wpw4CMplKh

• The SDK prints the following error message and closes the stream:

[restate] [2024-02-08T14:05:08.594Z] ERROR: Error while handling connection: Error: Unsupported protocol version 1, only version 0 is supported

[StephanEwen]

I think that is fine. Having a proper error on the runtime side would be even nicer, but this is ok for now, SDK side it prints correctly.

[StephanEwen]

To have a proper error on the runtime side as well, we would need to change the following:

• In the SDK, where we get the request path, we don't immediately respond with 200, 404, etc., but we read the first chunk of bytes, like a header message and interpret that.
• If that has a protocol mismatch, we send an appropriate status code and error message
• Otherwise we start setting up the connection to read the actual Restate stream messages