Add custom hook to specify successful publish message

[heavyimage]

Really minor hook-breakout here but it'd be nice to be able to control that message from a hook.

[manneohrstrom]

Thanks Jesse! Most of our team is out this week but i'll run this past the group next week and we can merge it in and release! Cheers! 👍 🍰 🎏

[heavyimage]

No sweat! Excited to contribute, even if it's something minor.