[FEATURE] Implementation for anyOf

[setime]

The schema anyOf is not implemented. This leads wrong schemas for values with anyOf and parsing issues.

Add a condition for anyOf in the function generatePropertiesContent() in the file swagger_models_generator.dart. Create the function generatePropertyContentByAnyOf() similar to generatePropertyContentByAllOf().

[wolru]

Same here. It is converted into dynamic.

{"anyOf": [{"type": "string"}, {"type": "null"}], "title": "Phone Number"}}
=> final dynamic phoneNumber;