Allow command execution on brew complete.

[freausan]

The servercommands: in config is useful for executing commands on drink, but the ability to execute a command when your brew completes would be stellar.

I have seen Denizen solutions, but this feels like a feature that would fit nicely in as a base feature.

Would be nice for integration with skilling plugins, leaderboard tracking, quest plugins, Skript, etc.

(having trouble finding where to put the label on the issue, but this would be an Enhancement)