Completes the service implementation of the transportv1.Service.
Ensures that both SSH and SSH Agent protocols are multiplexed
correctly over the gRPC stream via TestService_ProxySSH.
Part of #19812
Provides a client that can be used to connect to and interact with
the transport service in `lib/srv/transport`. The client abstracts
the fact that a gRPC stream is being used for the `net.Conn` created
by `DialCluster` and `DialHost`.
This also moves `lib/utils/grpc/stream` to `api/utils/grpc/stream`
so that the client and server can make use of the same stream
abstractions.
Part of #19812
The first step in implementing the teleport.proxy.v1.ProxyServic
as defined in RFD 100. This includes part of the service
implementation and a stream abstraction to allow transporting
payloads for frames over a gRPC stream.
The proxy peering specific implementation of the stream abstraction
was refactored into `lib/utils/grpc/stream` so that other services
can make use of it.
Part of #19812
* create package to contain proxy peering code
* Refactor proxy routing logic into a reusable object
Routing logic existed within an unexported handler of ssh subsystem
requests, which prevented it from being reused by other components
within the proxy, like the webapi server. This causes significant
latency issues for web sessions because the web apiserver is required
to dial the proxy ssh server to determine how to route to the host.
Since the web apiserver and the proxy ssh server exist in the same
process this is an entirely unnecesarry step that could be avoided
if the routing and ability to established connections were shared
throughout the proxy.
A new `proxy.Router` object is introduced which contains all the
logic that used to exist in `regular.proxySubsys` for determining
how to connect to servers and clusters. All routing within the
`regular.proxySubsys` now leverages the `proxy.Router` to dial
the target.
This is step 1 in addressing #15167. Now that the `proxy.Router`
exists `web.APIServer` will be able to make use of it to avoid
dialing the same process to establish connections.
rosstimothy