CDB3-328 CDB3-327 dgf-dutch/english 'prolongation.reason' field should be required in Swagger

Summary: make field required

X-Request-ID: c7a3ab77-3be1-4f4f-8b4b-90d8ce9118fb

Actual result: field is required in API - https://prnt.sc/vp6oes

Expected result: should be marked (*) in Swagger doc