v0.12.0

Custom runner labels, and a rename command

register and the pools file now take --labels, appended to the base set
every runner already carries. Until now the only way to add one was to
edit a pool's config by hand, after which nothing could see it and any
recreate dropped it silently. runpool pools shows them.

runpool rename moves a pool and re-registers its runners
under the new name.

Two things to know on upgrading. The pool name is one of its runners'
labels, so renaming a pool breaks any workflow using
runs-on: [self-hosted, ]. And absent --labels in the pools file now
means no extra labels: if you added one to a config by hand, declare it
in the file before your next apply, or apply will take it away. runpool
pools will show you what a pool currently carries.