python: copy the current Python generator into a "pydantic v1" generator (#16656)

* Copy the current Python generator into a "pydantic v1" generator

This generator will be deprecated over time and the normal generator will
focus on Pydantic v2.

* add missing doc

samples/client/echo_api/python-pydantic-v1/test/test_query.py

@@ -0,0 +1,56 @@
+# coding: utf-8
+
+"""
+    Echo Server API
+
+    Echo Server API
+
+    The version of the OpenAPI document: 0.1.0
+    Contact: team@openapitools.org
+    Generated by OpenAPI Generator (https://openapi-generator.tech)
+
+    Do not edit the class manually.
+"""  # noqa: E501
+
+
+import unittest
+import datetime
+
+from openapi_client.models.query import Query  # noqa: E501
+
+class TestQuery(unittest.TestCase):
+    """Query unit test stubs"""
+
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        pass
+
+    def make_instance(self, include_optional) -> Query:
+        """Test Query
+            include_option is a boolean, when False only required
+            params are included, when True both required and
+            optional params are included """
+        # uncomment below to create an instance of `Query`
+        """
+        model = Query()  # noqa: E501
+        if include_optional:
+            return Query(
+                id = 56,
+                outcomes = [
+                    'SUCCESS'
+                    ]
+            )
+        else:
+            return Query(
+        )
+        """
+
+    def testQuery(self):
+        """Test Query"""
+        # inst_req_only = self.make_instance(include_optional=False)
+        # inst_req_and_optional = self.make_instance(include_optional=True)
+
+if __name__ == '__main__':
+    unittest.main()