Add non-bidirectional stream methods

[fracek]

Is your feature request related to a problem? Please describe.
Using bidirectional streams is great to reconfigure streams on the fly, but it also means the streams are impossible to use with grpc-web.

Describe the solution you'd like
Add an additional method to stream data with an unidirectional stream. The client sends the configuration that will be used for the entirety of the stream.

Additional context
This is needed by Dojo.

[ptisserand]

Hi, I would like to work on this issue