[native/iOS] initialize database on app start

Summary:
This code will initialize db on iOS.
Context in ENG-2071

Test Plan:
Tested on simulator and iOS.

1. Created malformed db (e.g. simulate bug described in ENG-1910)
2. Open the app - should be terminated
3. Open again - app should delete database and perform soft-logout and continue running with proper structure

Reviewers: marcin, tomek

Reviewed By: marcin, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5996