Code refactoring (#889)

* Add __all__ to all module and plugin utils.

* Convert quite a few positional args to keyword args.

* Avoid Python 3.8+ syntax.

plugins/action/openssl_privatekey_pipe.py

@@ -52,7 +52,7 @@ class PrivateKeyModule:
                     module.fail_json(msg=f"Cannot decode Base64 encoded data: {e}")
             else:
                 data = to_bytes(content)
-            module_backend.set_existing(data)
+            module_backend.set_existing(privatekey_bytes=data)
 
     def generate(self, module: AnsibleActionModule) -> None:
         """Generate a keypair."""