f-string formatting and modify samples/recover_purge_operations.py

[eqvyoo]

azure-sdk-for-python/sdk/keyvault/azure-keyvault-keys/samples/recover_purge_operations.py

Is your feature request related to a problem? Please describe.
format을 f-string으로 바꾸고, 바로 purged된다는 것을 알려줘 가독성을 높일 수 있을 것 같습니다.

print("Purged '{}'".format(key_name))

Describe the solution you'd like

print("Purged f'{key_name}' immediately.")

Describe alternatives you've considered
Keys will be purged eventually but calling purge_deleted_key will purge keys right now.
Changing .format into f'{}' will increase readability.

Additional context