Shorten every instance of "CHANNEL" to "C" and whisper too

To save a little space in messages, it's getting very cramped

Modules/Commander.lua

@@ -307,7 +307,7 @@ function shared.Commander.Init()
 					for _, message in ipairs(messages) do
 						---@type Message
 						local msg = {
-							channel = "CHANNEL",
+							channel = "C",
 							data = channelname,
 							message = message
 						}