feat: add API endpoint for updating multiple targets
- Add an endpoint for creating/updating/deleting multiple Targets in one go, so that the frontend may submit one list
- For this purpose, an additional serializer was created that is used for this specific purposeS
- Supports creates, updates and deletes in a transaction
- For clarity, when creating or updating a new Target, take the
proposal_id
from the route param - Hopefully enough test coverage
Edited by Robbie Luijben