[WIP] Add get cmd for Pulsar functions

[wolfstudy]

Add get cmd for Pulsar functions

USED FOR:
    Fetch information about a Pulsar Function

REQUIRED PERMISSION:
    This command requires super-user permissions.

EXAMPLES:
    #Fetch information about a Pulsar Function
    pulsarctl functions get
	--tenant public
	--namespace default
	--name <the name of Pulsar Function>

    #Fetch information about a Pulsar Function with FQFN
    pulsarctl functions get
	--fqfn tenant/namespace/name [eg: public/default/ExampleFunctions]

OUTPUT:
    #normal output
    {
      "tenant": "public",
      "namespace": "default",
      "name": "test-functions",
      "className": "org.apache.pulsar.functions.api.examples.ExclamationFunction",
      "inputSpecs": {
        "persistent://public/default/test-topic-1": {
          "isRegexPattern": false
        }
      },
      "output": "persistent://public/default/test-topic-2",
      "processingGuarantees": "ATLEAST_ONCE",
      "retainOrdering": false,
      "userConfig": {},
      "runtime": "JAVA",
      "autoAck": true,
      "parallelism": 1,
      "resources": {
        "cpu": 1.0,
        "ram": 1073741824,
        "disk": 10737418240
      },
      "cleanupSubscription": true
    }

    #You must specify a name for the Pulsar Functions or a FQFN, please check the --name args
    [✖]  you must specify a name for the function or a Fully Qualified Function Name (FQFN)

    #The name of Pulsar Functions doesn't exist, please check the --name args
    [✖]  code: 404 reason: Function <your function name> doesn't exist

Usage: pulsarctl functions get [flags]

Aliases: get, get

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