Perform validation for all sets and filtering condition endpoints.

Perform validation for all sets and filtering condition endpoints and adjust proper error handling.
See Front-End validation scenarios in ticket UIOAIPMH-12.
Two more back-end scenarios:
1. Scenario - Filtering conditions list validation success

• Given set creation/modification
• When checking set filtering conditions
• And all filtering conditions fields are different, i.e. there are no similar fields, like Location and Location
• Then set can be saved to the database

2. Scenario - Filtering conditions list validation error

• Given set creation/modification
• When checking set filtering conditions
• And there are similar fields (like Location and Location) in two or more conditions for one set
• Then set can not be saved to the database
• And the message "Set can not have similar fields in its filtering conditions" is returned

Uniqueness validation will be done in scope of MODOAIPMH-220.