[REQ][PYTHON-FASTAPI] Generate Synchronous Python Fastapi Server

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

The python-fastapi generator only generates asynchronous server code, and there is no option to generate synchronous server code.

Describe the solution you'd like

Since FastAPI supports both asynchronous and synchronous programming, it would be valuable if the OpenAPI Generator could choose which one to generate (if sync or async).

Currently, when using the python-fastapi generator for the server, it does not provide an option to generate both async and sync implementations. It only generates asynchronous code for the server.

In contrast, the python generator for the client allows flexibility in choosing between synchronous and asynchronous implementations depending on the selected HTTP library. For example, when generating code with urllib3 library, the client code is generated as synchronous, whereas when generating it with asyncio library, the client code is generated as asynchronous.

Start by locating the python-fastapi server generator, its generation options, and the templates that currently produce asynchronous code. Compare its configuration with the python client's synchronous and asynchronous library choices. Done means users can select synchronous or asynchronous FastAPI output and the generated server consistently follows that choice.