Determine teams via command, rather than labels?

[RalfJung]

I regularly see people having to re-start the rfcbot process because an issue was labeled e.g. "T-compiler T-lang" but the FCP was meant for the lang team only. I myself sometimes forget to set a label at all before starting the process.

Maybe it would make sense to make the command rfcbot merge <list of teams> rather than inferring that from the labels?