admin-only messages

Value

• as the admin of a high-volume channel in the middle of chaotic circumstances, i want a way to be able to message other admins about how to make decisions about incoming info without having to leave the channel (eg: to talk to other admins on a separate signal thread)
• furthermore, without this ability, new admins frequently mistakenly send broadcast messages to the entire group thinking that only admins can see them
• it would be nice to provide a safe in-channel method to let admins talk to each other

Behavior

GIVEN a channel with admins alice, bob, and cassie plus 1000 subscribers

• WHEN alice sends a message that says ADMINS the money stash is below my bed
• THEN bob and cassie will get the message, but no subscribers will get it