CDB3-3538 Redemption relatedEntities validation

https://procedure-dev.prozorro.sale/api/jobber/redemption/jrs/63a2e0fa8168181e81a4aa8b

1. Add validation - only 1 asset in relatedEntities schema
2. Fix swagger - change schema to the same as announcement (list, without readOnly, minItems: 1, maxItems: 1)