Werk #18062: Fix 404 error code in site create, update and delete endpoints

Component	REST API
Title	Fix 404 error code in site create, update and delete endpoints
Date	May 31, 2025
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.5.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.4.0p3 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.3.0p34 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Ultimate MT

The endpoints for creating, updating, and deleting sites were returning a 404 error code instead of a 400 error code in case of validation errors.

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