This PR introduces the `linkerd alpha stat` command which will eventually replace the `linkerd stat` command. This command functions in a similar way, but with slightly different arguments and is implemented using the smi-metrics API. This means that access to metrics can be controlled with RBAC.
See the `linkerd alpha stat` help text for full details, or try one of these commands:
* `linkerd alpha stat -n emojivoto deploy/web`
* `linkerd alpha stat -n emojivoto deploy`
* `linkerd alpha stat -n emojivoto deploy/web --to deploy/emoji`
Signed-off-by: Alex Leong <alex@buoyant.io>