addChannel
Registers channel and writes its schema entry to the sink right away.
The entry holds the channel name and the full schema for its type.
Return
Parameters
T
The type of objects written to this channel
channel
The channel to add
Throws
if the channel belongs to a different log writer
Returns this writer's channel with the same name as channel.
If there is none, this registers a new WriterChannel with channel's name and schema and writes its schema entry.
Return
A WriterChannel bound to this writer
Parameters
T
The type of objects written to this channel
channel
The channel to look up or add