[2.3.0] Checkmk Werk 16292 created: user_config: add verification for contact groups and locked attributes

[//]: # (werk v2) # user_config: add verification for contact groups and locked attributes key | value ---------- | --- date | 2024-01-16T14:42:21+00:00 version | 2.3.0b1 class | fix edition | cre component | rest-api level | 1 compatible | yes This werk introduces two changes: * it now verifies for create & edit if the provided contact groups actually exist * it verifies that for an edit request, locked attributes are not being modified