ZEVA2 - Initiative and Purchase Agreements #93 - DB Schema

**Description**
Create the basic Prisma schema and modify the seed file for the Initiative and Purchase Agreement.
This is a part of the user story #93

**Acceptance Criteria**
- [ ] Having basic Prisma schema (tables, relationships, constraints) for Initiative and Purchase Agreement
- [ ] Able to transfer existing ZEVA1 data to the new tables

**Notes**
The database structure may differ from that of ZEVA-1, depending on what would make sense for the rebuild.