Update ansible-core to be an option dependency

Removes restriction on destination environment, allowing users to use
the same version of ansible with this script as they use for everything else

vault2vault.py

@@ -12,10 +12,17 @@ from typing import List
 from typing import Tuple
 from typing import Union
 
-import ansible.constants
-import ansible.parsing.vault
 import ruamel.yaml
 
+try:
+    import ansible.constants
+    import ansible.parsing.vault
+except ImportError:
+    print(
+        "FATAL: No supported version of Ansible could be imported under the current python interpreter"
+    )
+    sys.exit(1)
+
 
 __title__ = "vault2vault"
 __summary__ = "Recursively rekey ansible-vault encrypted files and in-line variables"