Add flag for subject version permanent delete

[rsolovev]

The SchemaRegistryClient delete_version() function does not have ?permanent=true functionality mentioned in Schema Registry API reference - https://docs.confluent.io/platform/current/schema-registry/develop/api.html#delete--subjects-(string-%20subject)-versions-(versionId-%20version)

confluent-kafka-python/src/confluent_kafka/schema_registry/schema_registry_client.py

Lines 563 to 585 in 370d62e

	def delete_version(self, subject_name, version):
	"""
	Deletes a specific version registered to ``subject_name``.
	Args:
	subject_name (str) Subject name
	version (int): Version number
	Returns:
	int: Version number which was deleted
	Raises:
	SchemaRegistryError: if the subject or version cannot be found.
	See Also:
	`Delete Subject Version API Reference <https://docs.confluent.io/current/schema-registry/develop/api.html#delete--subjects-(string-%20subject)-versions-(versionId-%20version)>`_
	""" # noqa: E501
	response = self._rest_client.delete('subjects/{}/versions/{}'.
	format(_urlencode(subject_name),
	version))
	return response

Added flag support similar to delete_subject() implementation and taking into the account this documentation lines:

The default is false. If the flag is not included, a soft delete is performed. You must perform a soft delete first, then the hard delete.

[cla-assistant]

All committers have signed the CLA.

[rayokota]

Subsumed by #1867