Add stop cmd for Pulsar Functions

[wolfstudy]

Signed-off-by: xiaolong.ran ranxiaolong716@gmail.com

Add stop cmd for Pulsar Functions, the output as follows:

USED FOR:
    This command is used for stopping function instance.

REQUIRED PERMISSION:
    This command requires super-user permissions.

EXAMPLES:
    #Stops function instance
    pulsarctl functions stop
	--tenant public
	--namespace default
	--name <the name of Pulsar Function>

    #Stops function instance with instance ID
    pulsarctl functions stop
	--tenant public
	--namespace default
	--name <the name of Pulsar Function>
	--instance-id 1

    #Stops function instance with FQFN
    pulsarctl functions stop
	--fqfn tenant/namespace/name [eg: public/default/ExampleFunctions]

OUTPUT:
    #normal output
    Stopped successfully

Usage: pulsarctl functions stop [flags]

Aliases: stop, stop

FunctionsConfig flags:
      --fqfn string          The Fully Qualified Function Name (FQFN) for the function
      --tenant string        The tenant of a Pulsar Function
      --namespace string     The namespace of a Pulsar Function
      --name string          The name of a Pulsar Function
      --instance-id string   The function instanceId (stop all instances if instance-id is not provided)

[wolfstudy]

@sijie @zymap PTAL