WIP add new var to re-enable legacy behavior

Author: ctreatma

modules/openapi-generator/src/main/resources/python-fastapi/model_generic.mustache

@@ -260,15 +260,15 @@ class {{classname}}({{#parent}}{{{.}}}{{/parent}}{{^parent}}BaseModel{{/parent}}
         if not isinstance(obj, dict):
             return cls.model_validate(obj)
 
-        {{#disallowAdditionalPropertiesIfNotPresent}}
+        {{^vendorExtensions.x-py-legacy-additional-properties-validation}}
         {{^isAdditionalPropertiesTrue}}
         # raise errors for additional fields in the input
         for _key in obj.keys():
             if _key not in cls.__properties:
                 raise ValueError("Error due to additional fields (not defined in {{classname}}) in the input: " + _key)
 
         {{/isAdditionalPropertiesTrue}}
-        {{/disallowAdditionalPropertiesIfNotPresent}}
+        {{/vendorExtensions.x-py-legacy-additional-properties-validation}}
         _obj = cls.model_validate({
             {{#allVars}}
             {{#isContainer}}

modules/openapi-generator/src/main/resources/python-pydantic-v1/model_generic.mustache

@@ -252,15 +252,15 @@ class {{classname}}({{#parent}}{{{.}}}{{/parent}}{{^parent}}BaseModel{{/parent}}
         if not isinstance(obj, dict):
             return {{{classname}}}.parse_obj(obj)
 
-        {{#disallowAdditionalPropertiesIfNotPresent}}
+        {{^vendorExtensions.x-py-legacy-additional-properties-validation}}
         {{^isAdditionalPropertiesTrue}}
         # raise errors for additional fields in the input
         for _key in obj.keys():
             if _key not in cls.__properties:
                 raise ValueError("Error due to additional fields (not defined in {{classname}}) in the input: " + obj)
 
         {{/isAdditionalPropertiesTrue}}
-        {{/disallowAdditionalPropertiesIfNotPresent}}
+        {{/vendorExtensions.x-py-legacy-additional-properties-validation}}
         _obj = {{{classname}}}.parse_obj({
             {{#allVars}}
             {{#isContainer}}

modules/openapi-generator/src/main/resources/python/model_generic.mustache

@@ -279,15 +279,15 @@ class {{classname}}({{#parent}}{{{.}}}{{/parent}}{{^parent}}BaseModel{{/parent}}
         if not isinstance(obj, dict):
             return cls.model_validate(obj)
 
-        {{#disallowAdditionalPropertiesIfNotPresent}}
+        {{^vendorExtensions.x-py-legacy-additional-properties-validation}}
         {{^isAdditionalPropertiesTrue}}
         # raise errors for additional fields in the input
         for _key in obj.keys():
             if _key not in cls.__properties:
                 raise ValueError("Error due to additional fields (not defined in {{classname}}) in the input: " + _key)
 
         {{/isAdditionalPropertiesTrue}}
-        {{/disallowAdditionalPropertiesIfNotPresent}}
+        {{/vendorExtensions.x-py-legacy-additional-properties-validation}}
         _obj = cls.model_validate({
             {{#allVars}}
             {{#isContainer}}