Add an edge table to the search database

Summary:
Fixes T10778. This is a result of T10262: when we save a form configuration and adjust the policy, we try to scramble attached file secrets.

There aren't going to be any attached files, but there's also no edge table, so we fail.

We could skip this code, but we'll likely need an edge table here sooner or later so it's probably simpler in the long run to just add an empty one.

Test Plan:

• Ran bin/storage upgrade, got a clean bill of health.
• Saved a form configuration after making a policy edit, no more edge exception.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10778

Differential Revision: https://secure.phabricator.com/D15803