Imports of package metrics

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
github.com/docker/go-events
github.com/docker/go-metrics
github.com/moby/swarmkit/v2/api
github.com/moby/swarmkit/v2/manager/state/storePackage store provides interfaces to work with swarm cluster state.
stringsPackage strings implements simple functions to manipulate UTF-8 encoded strings.