Priming the entity_usage table based on page-props.

This hooks up automatic population with the schema updater.

Bug: 73220
Change-Id: Ie38eaf847b4349a2d84d9cfef2fe3bbcad684eca
Maintenance script for populating wbc_entity_usage

Bug: T73050
Change-Id: I9e99723d90478d37ea30a63aa39d507763d0dfff
Merge "Priming the entity_usage table based on page-props."
Merge "Maintenance script for populating wbc_entity_usage"