add action create --copy

**Is your feature request related to a problem? Please describe.**
Sometimes, it is convenient to create an action by copying an other. The `wsk` cli supports `wsk action create newAction --copy oldAction` as an example.

**Describe the solution you'd like**
Allow action create with --copy as convenience to copying an existing action to a new name.

**Describe alternatives you've considered**
The alternative is to manually get the action, and save the code, params and annotations to files then recreate the action.