unsubscribeFromChannel
Unsubscribe from a specific channel.
This method allows a user to unsubscribe from the given channel. Once unsubscribed, the user will stop receiving notifications and updates related to the channel's content.
Return
A RainbowResult indicating the success or failure of the operation. In case of failure, the result will contain error details.
Parameters
channel
The Channel object from which the user will unsubscribe.