Provide the customwebhookbot.py example with different frameworks

[clot27]

What kind of feature are you missing? Where do you notice a shortcoming of PTB?

Currently, we provide an example of setting up a custom webhook for bots using Starlette. While this helps many people write their own custom webhook implementations, we also frequently receive questions about Flask and Django in our Telegram group. People face difficulties writing their own custom webhook implementations with these frameworks because they have to manage the startup-execution-shutdown logic on their own (see also this wiki section).

Describe the solution you'd like

Adding variaents of the customwebhookbot.py example to the documentation for those two frameworks and other well known webserver frameworks would help people better understand how to integrate them with PTB.

Describe alternatives you've considered

No response

Additional context

It would be a cool UX improvement to allow users to choose the framework in the rendered documentation.