send enforcement action for override decisions

[eviljeff]

Fixes: mozilla/addons#15371

Description

Trivial change to now send enforcement action too for an override decision, with some clean-up because now all decision endpoints accept the same action and policies fields.

Testing

Pretty trivial change, but to test:

• set your setting CINDER_SERVER_URL to https://mozilla-staging.cinderapp.com/api/v1/ (until update CINDER_SERVER_URL to saas cinder #23709 is merged)
• in reviewer tools force disable a recommended add-on
• in 2nd level approval queue in reviewer tools, requeue the add-on in the reviewer tools
• back in reviewer tools, resolve the (newly created, from requeue) job, but this time reject the a version instead of disable
• check in fake mail for the email to the developer about the rejection
• check in Cinder that the override decision has the enforcement action of amo-reject-version-addon rather than amo-disable-addon.

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.