Store OPTIONS requests into viewset's self.action

[normanjaeckel]

At the moment, self.action is None in viewsets if I get an OPTIONS request. I think I can inspect self.request.method.lower() but it would be nice if it is also in self.actions so I can use it as generic point for customized viewset code (customized permission checks in our case: OpenSlides/OpenSlides#1595).

[lovelydinosaur]

Reopening this until 538ffaf has been addressed.

[catskul]

I believe I've fixed it here:
#3158

[lovelydinosaur]

And, resolved again.