Support plugin service API calls from Go client

[tharinduwijewardane]

Is your feature request related to a problem? Please describe. Cannot create/update retention scripts programmatically

Describe the solution you'd like Add the support to call plugin service API from Go SDK

Describe alternatives you've considered

Additional context

[tharinduwijewardane]

This can be achieved by adding cloudpb.PluginServiceClient to the VizierClient struct

@aimichelle @zasgar Is this acceptable ?

[aimichelle]

Hi @tharinduwijewardane ! Thanks for the suggestion! Registering plugin scripts is an operation done through the cloud, so it would actually make most sense to add it to the cloud client operations instead, and initialize the client here (see cmClient).

[tharinduwijewardane]

I will send a PR soon