Issue 1766 Modified mustache files for Go to support nullable in the … (#1869)

* Issue 1766 Modified mustache files for Go to support nullable in the spec v3.0+; Updated model files running .sh scripts for Go.

* Add "nullable" to fake yaml

* Add sample script for OAS3

* Fix output folder (openapi3)

* Run bin/openapi3/go-petstore.sh

* Update samples

* Update jaxrs-jersey

* Update python and php samples

* Add bin/openapi3/go-gin-petstore-server.sh

* Run bin/openapi3/go-gin-petstore-server.sh

* Update bin/openapi3/go-petstore-server.sh to generate "nullable" samples

* Run bin/openapi3/go-petstore-server.sh

* Fix duplicated `import`

samples/openapi3/client/petstore/python/test/test_health_check_result.py

@@ -0,0 +1,39 @@
+# coding: utf-8
+
+"""
+    OpenAPI Petstore
+
+    This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\  # noqa: E501
+
+    OpenAPI spec version: 1.0.0
+    Generated by: https://openapi-generator.tech
+"""
+
+
+from __future__ import absolute_import
+
+import unittest
+
+import petstore_api
+from petstore_api.models.health_check_result import HealthCheckResult  # noqa: E501
+from petstore_api.rest import ApiException
+
+
+class TestHealthCheckResult(unittest.TestCase):
+    """HealthCheckResult unit test stubs"""
+
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        pass
+
+    def testHealthCheckResult(self):
+        """Test HealthCheckResult"""
+        # FIXME: construct object with mandatory attributes with example values
+        # model = petstore_api.models.health_check_result.HealthCheckResult()  # noqa: E501
+        pass
+
+
+if __name__ == '__main__':
+    unittest.main()