R1:9a7383121dbb

Move cancel/retry/free task queue actions to bin/worker

Summary:
Fixes T6702. Ref T3554. Currently, tasks can be cancelled, retried and freed from the web UI by any logged in user.

This isn't appreciably dangerous (I can't come up with a way that a user could do anything security-affecting), but I think I probably intended this to be admin-only, but these actions should move to the CLI anyway.

Move them to the CLI. Lay some groundwork for some future `bin/worker cancel --class SomeTaskClass`, but don't…