[REQ] add support for decimals in the python generator

Created by: rizwansaeed

Describe the solution you'd like

Add support to the python generator for the following:

units:
  type: string
  format: decimal

which would generate a field of type decimal.Decimal that is de/serialized across the wire as a string.

I am aware that support has been added to the python-experimental as part of https://github.com/OpenAPITools/openapi-generator/pull/11282 but we are looking for support in the python generator.

We'd be happy to raise a PR but are looking for a steer on what the required changes would be and how long it might take to implement.

Thanks