R1:77bcbed9f98e

Implement PolicyAwareQuery for triggers

Summary:
Ref T6881. I tried to cheat here by not implementing this, but we need it for destroying triggers directly with `bin/remove destroy`, since that needs to load them by PHID.

So, cheat slightly less. Implement PolicyAware but not CursorPagedPolicyAware.

Test Plan:
- Used `bin/remove destroy` to destroy a trigger by PHID.
- Browsed daemon console.
- Ran trigger daemon.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

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