Multiple http methods per action in schema

[Nnonexistent]

Description

See #4391

Problem with schema generation for this kind of statements:

    @detail_route(methods=['put', 'post'])
    def custom_action(self, request, pk):
        ...

[tomchristie]

Okay, we're not going to be able to address this use-case, since there's no way for us to differentiate between the two methods. On the backlog to review the most graceful way to handle it, but ultimately multiple methods are not going to be a style we can support.

[tomchristie]

Possibly also be an issue with function based views with multiple methods.

[Nnonexistent]

Add suffix (http method name) for actions with identical category+action.

[Nnonexistent]

I dug through coreapi-codec and find that it doesn't use action keys at all while generating paths object (openapi_codec.encode._get_paths_object).
So we can name our actions in coreapi documents as we want as far they are unique.

If so, this patch should fix problem with no side effects.

[tomchristie]

Closed via #4529. Incoming in version 3.5