support oamctl trait-list

[wonderflow]

$ oamctl trait-list
NAME            VERSION PRIMITIVES                                                              
--------        ------- ----------                                                              
autoscaler      v1.0.0  core.oam.dev/v1alpha1.Server, core.oam.dev/v1alpha1.Task                
empty           v1.0.0  *                                                                       
ingress         v1.0.0  core.oam.dev/v1alpha1.Server, core.oam.dev/v1alpha1.SingletonServer     
manual-scaler   v1.0.0  core.oam.dev/v1alpha1.Server, core.oam.dev/v1alpha1.Task                
volume-mounter  v1.0.0  core.oam.dev/v1alpha1.Server, core.oam.dev/v1alpha1.SingletonServer, core.oam.dev/v1alpha1.Worker, core.oam.dev/v1alpha1.SingletonWorker, core.oam.dev/v1alpha1.Task, core.oam.dev/v1alpha1.SingletonTask

fixes part of #2

[hongchaodeng]

lgtm