Ingest BT channel metadata

Extra information is stored as channel groups, retrieved
from BT's MPX system.

Configuration remains to be done, once we have the various
environments from them.
you fetch the freeview platform directly in the ``runTask`` method, and throw here, but for the BT channel group, you throw in a nested method. IMO it'd be nicer if both were done either in ``runTask`` or in a method, as at a glance it appears as though you fetch and check one but not t'other