chore: add helper for checking constraint violation DB errors

[jakedoublev]

Addresses: #81

Adds helper functions for the db layer across tables for:

1. unique constraint violations
2. not null violations
3. foreign key violations
4. restrict violations (not used yet but may be if we prevent DELETE on certain tables and go to active/inactive state)
5. not found errors

[jrschumacher]

Could you also add constraint checks for:

• insert or update FK constraint
• deleting or updating FK constraint