check for async callable object and function for relay resolver

[reallistic]

This PR ensures that the relay resolve_wrapper can handle async functions and objects with an async __call__ method.

I ran into this issue trying to use the ariadne-auth authz.require_permission function alongside the connection class.
require_permission converts the decorated resolver into an instance of PermissionChecker which defines an async __call__ and is not picked up by inspect.iscoroutinefunction.

The helper function was inspired by starlette.

For now, I only added the helper to the connection object, that said, many of the existing usages of inspect.iscoroutinefunction will want to move to this helper.