Add support for launcher recheck

[directionless]

We got a customer request for a command line way to trigger a recheck, they like to do this without a web browser.

My memory is we got most of the way through building this, and then decided the control server async polling wasn't a great UI and abandoned it. But, I think it's worth a quick revisit here.

I think:

1. launcher recheck should send a recheck message, same path the restart messages take
2. We can update K2 to accept this and recheck failing checks