Is your feature request related to a problem? Please describe.

Given a 2.0 OpenAPI document, trying to import it fails as it finds no models

Args:

--input-file-type openapi --input openapi/ProductSearch.json --output doc_insights/openapi/product_search.py --openapi-scopes schemas

Describe the solution you'd like
Auto-detection of the v2 api via the "swagger": "2.0" or "openapi": "2.0" part (or a cli flag).

Then under v2 mode, load definitions instead of components.schemas

So
https://github.com/koxudaxi/datamodel-code-generator/blob/2df133c00949b6efce6f1493c6ce0e341872b955/datamodel_code_generator/parser/openapi.py#L586C13-L588
would turn into

schemas: Dict[Any, Any] = specification.get('definitions', {})

Making this change works for me, but there might be other v2/v3 incompatibilities that my use case doesn't run into.

Describe alternatives you've considered
It doesn't look like there is a way to load v2 OpenAPI docs in this tool, I also don't have control over the spec so I can't update it to v3.