pkg/k8s.Watcher: Use a single stop channel
pkg/k8s.Watcher: Use a single stop channel

It isn't necessary to create a new channel for every worker process.

datawire/telepresence,datawire/ambassador,datawire/telepresence,datawire/ambassador,datawire/telepresence,datawire/ambassador,datawire/ambassador,datawire/ambassador