R1:b9568646ac00

Add an owners package generator for Lipsum

Summary: Ref T12319. Allow `bin/lipsum generate` to generate owners packages.

Test Plan: Generated ~4,000 packages with ~150,000 paths.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12319

Differential Revision: https://secure.phabricator.com/D17423