feat: generate "DB on main thread" issues

[armcknight]

Provide a way to generate large amounts of DB entities, so that subsequent fetches take long enough to cause "DB on main thread" issues.

I was able to see DB on Main Thread issues now after generating large amounts of db records and relaunching the app to load them all at once: https://demo.sentry.io/issues/4542023700/?project=6249899&query=is%3Aunresolved+se%3Aandrewmcknight&referrer=issue-stream&statsPeriod=14d&stream_index=0

Here's a quick demo of how to generate the items:

https://github.com/sentry-demos/ios/assets/3241469/5b3f4ee8-f54a-44ea-867d-29e164f0282a

There's also a launch argument you can use to immediately wipe the database if you find it's taking too long to launch the app and you want to start over (make sure not to commit the xcscheme file in git with this enabled):

closes #25

[armcknight]

I'm not seeing issues yet, even though it generates db spans that take multiple seconds, while the docs state 16 ms is enough.

See https://andrewsorg.sentry.io/performance/ios:9ce38952e35f46a8aa26bfc1b6c59a2e/?project=4505840007184384&query=&referrer=performance-transaction-summary&statsPeriod=14d&transaction=EmpowerPlantViewController&unselectedSeries=p100%28%29&unselectedSeries=avg%28%29

[kpujjigit]

Verified Working