Type overrides

[otonnesen]

Is your feature request related to a problem? Please describe.
At my work, we have a few custom pydantic models that aren't really easy or possible to encode in an OpenAPI spec. As a result, we define them as pydantic.StrictStr and end up doing a lot of annoying back-and-forth rote type conversions whenever we interact with them on any code-generated models.

Describe the solution you'd like
It would be great if we could just provide a mapping from OpenAPI spec model names to Python import strings and have datamodel codegen link to them instead. My rough idea for how this would work is to have a JSON file with the following structure:
type-overrides.json

{
  "Some.PotentiallyNamespaced.CodeGeneratedType": "my_app.some_module.types.MyType",
  ...
}

This file could then be passed in as a filename (similar to how --aliases is handled), like datamodel-codegen ... --type-overrides type-overrides.json.

Describe alternatives you've considered
Currently, we define complex models as pydantic.StrictStr and handle type conversions manually. This approach, however, is error-prone and requires a bunch of annoying boilerplate everywhere.

I briefly looked into trying to do this mapping with custom_templates, but it got ugly quick.

Additional context
I'd be willing to work on the change myself if there's any appetite to add the feature. I have a sorta-working WIP branch here: https://github.com/otonnesen/datamodel-code-generator/tree/experiment/type-overrides.