Provide sponsor_channel or similar server feature value.

[jessopb]

Hub operators should be able to include a channel to visit.
Creators would be incentivized to provide hubs, and their channels could show multiple donation methods.

The change appears to be in this file,

hub/hub/herald/env.py

Line 51 in 99e1006

self.description = description if description is not None else self.default('DESCRIPTION', '')

and this file:
https://github.com/lbryio/hub/blob/9b178222296aecc7699cf82141c7a48fe866f22a/hub/herald/session.py