upload
Upload an avatar for a specific channel.
This method allows you to upload a custom avatar image for a channel. The avatar will be associated with the channel and will be visible to all users who have access to the channel.
Return
A RainbowResult indicating the success or failure of the operation. If the operation succeeds, the result will contain no data (Unit). In case of failure, it will include error details.
Parameters
channel
The ID of the channel for which the avatar is being uploaded.
feed
A File object representing the avatar image to upload.