Update endpoint for creating/updating schedules

Currently the endpoint return the same HTTP Status Code when creating or updating a schedule results in conflicting timeslots.

We should return codes that reflect the status of the operation:

• a request to create a schedule should return a 201 (Created) status if the operation doesn't result in collisions in the timeslot or they can be solved with solutions offered,
• a request to create or update a schedule should return a 409 (Conflict) status if the operation results in collisions in the timeslots that need to be resolved.