Move connection owner admin notice

In the JITM package, there is some code for a notice that is displaying when attempting to disconnect the connection owner. Where that notice is hooked, the [following comment was written](https://github.com/Automattic/jetpack/blob/1f4935e91f76082ba242aa5cc75c4dc2f9cf5b7f/packages/jitm/src/class-jitm.php#L96):

> // Not really a JITM. Don't know where else to put this :) .

I'd like to suggest that we move that to one of the classes in the connection package since, in any plugin that uses the connection package, we'd likely want that notice to be displayed.