R1:d9bd062bba72

Fix an issue with viewing an empty board with milestone columns

Summary:
Ref T10010.

- Viewing an empty board with milestone columns did a meaningless edge query. Don't do that.
- When creating the first milestone of a parent, force the indexing engine to rematerialize it inline. This sets `hasMilestones` properly. Otherwise, the daemons may take some time to fix this in the indexer.

Test Plan:
- Viewed an empty board of a project with a milestone.
- Viewed a normal board.
- Created the first…