Add a forwarding import for ConsentRequirementHook.
Add a forwarding import for ConsentRequirementHook.

This exposes the new `ConsentRequirementHook` in Djblets in
`reviewboard.extensions.hooks`, making it easy for extension authors to
look up the entire list of hooks and pull them in from one place.

Testing Done:
Used this in an extension successfully.

Reviewed at https://reviews.reviewboard.org/r/9969/

chipx86/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard