codeintel: Run sqlite migrations in background
Created by: efritz
On the start of the bundle manager, kick off a pool of goroutines that will open then immediately shut a reader backed by SQLite files on disk. This helps run migrations out of band in case larger files take too long to perform in the query path.
This will be polished more in subsequent PRs (not running PRs when unnecessary, better catching errors about SQLite exclusivity locks, etc).