(feature) Limit the feeds for channels to subscribers only

When a user marks their channel as closed, we must update the feeds to only show to subscribers.

All posts in the feed will need to be marked with open and closed Changing a channel's open or closed endpoint will need to reindex the channel When a user requests a channel, we will need to provide a list of all channels they are subscribed too We will need to exclude any entity which belongs to a closed channel that they do not subscribe too