[2.3.0] Checkmk Werk 16037 created: folder_config/host_config: No longer accept non-existent site

[//]: # (werk v2) # folder_config/host_config: No longer accept non-existent site key | value ---------- | --- date | 2023-12-22T08:11:28+00:00 version | 2.3.0b1 class | fix edition | cre component | rest-api level | 1 compatible | yes You can no longer set a non-existent site on folders and hosts. When called with a non-existent site as an attribute the endpoints now return the status code 400.