R1:845a7d871666

Allow the PullLocal daemon to actually hibernate

Summary:
Ref T12298. The PullLocal daemon has had hibernation code for a little while, but it never actually activated because we don't sleep for more than 15 seconds in any case.

Add a maximum sleep instead and use that to control the longest sleep we'll do for hibernation purposes.

Also, when a repository or repository URI is edited, write a NEEDS_UPDATE event into the message table to make sure the daemons de-hibernate.

Test Plan: Used `bin/phd debug…