[python-nextgen] better datetime support in parameters (#14621)

* add allowStringInDateTimeParameters option

* add tests

* add files

* add tests for datetime query parameters

* fix file anme

* trigger build

* fix pytest

* install test requirement

* trigger build

* break build

* add new files

* fix Locale.ROOT

* update doc

samples/client/echo_api/python-nextgen/setup.py

@@ -0,0 +1,48 @@
+# coding: utf-8
+
+"""
+    Echo Server API
+
+    Echo Server API  # noqa: E501
+
+    The version of the OpenAPI document: 0.1.0
+    Contact: team@openapitools.org
+    Generated by: https://openapi-generator.tech
+"""
+
+
+from setuptools import setup, find_packages  # noqa: H301
+
+# To install the library, run the following
+#
+# python setup.py install
+#
+# prerequisite: setuptools
+# http://pypi.python.org/pypi/setuptools
+NAME = "openapi-client"
+VERSION = "1.0.0"
+PYTHON_REQUIRES = ">=3.7"
+REQUIRES = [
+    "urllib3 >= 1.25.3",
+    "python-dateutil",
+    "pydantic",
+    "aenum"
+]
+
+setup(
+    name=NAME,
+    version=VERSION,
+    description="Echo Server API",
+    author="OpenAPI Generator community",
+    author_email="team@openapitools.org",
+    url="",
+    keywords=["OpenAPI", "OpenAPI-Generator", "Echo Server API"],
+    install_requires=REQUIRES,
+    packages=find_packages(exclude=["test", "tests"]),
+    include_package_data=True,
+    license="Apache 2.0",
+    long_description_content_type='text/markdown',
+    long_description="""\
+    Echo Server API  # noqa: E501
+    """
+)