make async generic views

[amirreza]

hello
i'm very new to async so this might be very dumb or maybe not, i didn't find anything about it with google so might as well see

i think we should add async generic class based views

my reasons:
1- easy to use
2- makes writing docs and tutorials on async django easier
3- it can be used as a standard on how to write async class based views
4- can attract more devs to use and contribute to async django

also i think seprating normal gcbv and async ones can make the code easier to debug
also leaves less un-used code in classes
and makes learning this much easier for beginners

anyways i hope this is not dumb :) and can help django improve

[Mariusz Felisiak]

Class-based views already allow defining async method handlers, check out ​docs.