add new rpc endpoint

[majestrate]

llarp.async-exit command will reply with a llarp.notify-exit command with the same values as llarp.exit this can be used to bypass request timeoutes in omq

refactor internal bits in rpc to be a bit more dry (still wet af)

[majestrate]

rebased ontop of dev

[majestrate]

conflicts with #2121 so closing