[REQ] allow to pass a `str` to the Python aiohttp client

[ziodave]

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

At the moment, it is not possible but to use bytes to pass raw data to the client

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/python/asyncio/rest.mustache#L183

This conflicts with definitions that are string and represented as StrictStr in model.

Describe the solution you'd like

Same solution as in the sample here:

openapi-generator/samples/client/echo_api/python/openapi_client/rest.py

Line 220 in a4d43a8

elif isinstance(body, str) or isinstance(body, bytes):

[wing328]

closed via #18985