R1:9f56a014e2a8

Migrate existing projects to retain "Workboard" as default item

Summary:
Ref T10054. Ref T6961.

- Existing projects with workboards had "Workboard" as the default menu item. Retain this behavior.
- Populate the recently-added `hasWorkboard` flag so we can do a couple of things a little faster (see T6961).

Test Plan:
- Ran migration.
- Verified a bunch of projects looked sensible/correct after the migration.
- Created a workboard, verified `hasWorkboard` got set properly.

Reviewers: chad…