[client] add ability to list topic names which exist on the server

There is no way to list the topics available to be read

Pubsub and kafka libraries (ex. sarama) have this feature

We could list the topics using the pulsaradmin. Here is the API:

pulsar-client-go/pulsaradmin/pkg/admin/topic.go

Lines 43 to 44 in f476814

    
           // List returns the list of topics under a namespace 
        
           List(utils.NameSpaceName) ([]string, []string, error)

Is that OK for you?

@RobertIndie I think that's okay. Can you please clarify what to pass into the namespace? When I create a client pulsar.NewClient(...), what namespace does it use by default?

@jayshrivastava The default namespace is public/default.

	// List returns the list of topics under a namespace
	List(utils.NameSpaceName) ([]string, []string, error)