Making kubernetes executor ResourceVersion a self contained singleton

[amoghrajesh]

To make ResourceVersion a singleton, it doesn't have to import Singleton from utils. Using the __new__ pattern instead. Guidance from here: https://www.geeksforgeeks.org/python/singleton-pattern-in-python-a-complete-guide/

I will deprecate the singleton library from utils in a parallel PR.

Test to verify that it works fine before and after:

from airflow.providers.cncf.kubernetes.executors.kubernetes_executor_utils import ResourceVersion
rv1 = ResourceVersion()
rv2 = ResourceVersion()
rv3 = ResourceVersion()
rv1 == rv2 == rv3
Out[3]: True
rv1.resource_version["namespace1"] = "12345"
rv2.resource_version["namespace1"] == "12345"
rv3.resource_version["namespace1"] == "12345"
Out[4]: True
import gc
instances = [obj for obj in gc.get_objects()
             if type(obj).__name__ == 'ResourceVersion']
instances
Out[6]: [<airflow.providers.cncf.kubernetes.executors.kubernetes_executor_utils.ResourceVersion at 0x1119ea3c0>]

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