[python-fastapi] Default default value ... instead of None (#22494)

With various FastAPI parameters (Query, Path, Header, Cookie, Body,
Form, and File) the default value of None is a valid value, but
signifies that the parameter is optional.  To allow for required
parameters, default should either not be set at all or be set to '...'
(ellipsis).

Issue: #22494

Author: zhornback

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

@@ -1 +1 @@
-{{#isPathParam}}{{baseName}}{{/isPathParam}}{{^isPathParam}}{{paramName}}{{/isPathParam}}: {{>param_type}} = {{#isPathParam}}Path{{/isPathParam}}{{#isHeaderParam}}Header{{/isHeaderParam}}{{#isFormParam}}Form{{/isFormParam}}{{#isQueryParam}}Query{{/isQueryParam}}{{#isCookieParam}}Cookie{{/isCookieParam}}{{#isBodyParam}}Body{{/isBodyParam}}({{&defaultValue}}{{^defaultValue}}{{#isPathParam}}...{{/isPathParam}}{{^isPathParam}}None{{/isPathParam}}{{/defaultValue}}, description="{{description}}"{{#isQueryParam}}, alias="{{baseName}}"{{/isQueryParam}}{{#isLong}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isLong}}{{#isInteger}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isInteger}}{{#vendorExtensions.x-regex}}, regex=r"{{.}}"{{/vendorExtensions.x-regex}}{{#minLength}}, min_length={{.}}{{/minLength}}{{#maxLength}}, max_length={{.}}{{/maxLength}})
+{{#isPathParam}}{{baseName}}{{/isPathParam}}{{^isPathParam}}{{paramName}}{{/isPathParam}}: {{>param_type}} = {{#isPathParam}}Path{{/isPathParam}}{{#isHeaderParam}}Header{{/isHeaderParam}}{{#isFormParam}}Form{{/isFormParam}}{{#isQueryParam}}Query{{/isQueryParam}}{{#isCookieParam}}Cookie{{/isCookieParam}}{{#isBodyParam}}Body{{/isBodyParam}}({{&defaultValue}}{{^defaultValue}}{{#required}}...{{/required}}{{^required}}None{{/required}}{{/defaultValue}}, description="{{description}}"{{#isQueryParam}}, alias="{{baseName}}"{{/isQueryParam}}{{#isLong}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isLong}}{{#isInteger}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isInteger}}{{#vendorExtensions.x-regex}}, regex=r"{{.}}"{{/vendorExtensions.x-regex}}{{#minLength}}, min_length={{.}}{{/minLength}}{{#maxLength}}, max_length={{.}}{{/maxLength}})