Is the SSH user name accessible by the ChannelHandler?

A server may care about which user has connected. I'm not seeing a path to connect the SSH user name to any of my handler code. I'm not even seeing it saved and available in `SSHChildChannel` or anything hanging off of it.

Unless I've missed something this will take some doing to add. Options include:

- Adding a `SSHChannelRequestEvent` with a description of the user name which is sent first.

- `NIOSSHHandler()` could get a new initializer which passes authentication information into the `inboundChildChannelInitializer:` equivalent.

Either of these presuppose that the user name is saved somewhere.

Start by tracing how authentication information reaches SSHChildChannel and whether the user name is retained there. Compare the proposed SSHChannelRequestEvent and NIOSSHHandler initializer approaches, including inboundChildChannelInitializer:, and finish when handler code can access the authenticated SSH user name through a documented, tested path.

Written by the indexing model from the issue text.