[2.3.0] Checkmk Werk 16207 created: host_tag_group: Fix 500 status code when creating a host_tag_group with id already in use

Title: host_tag_group: Fix 500 status code when creating a host_tag_group with id already in use Class: fix Compatible: compat Component: rest-api Date: 1702550742 Edition: cre Level: 1 Version: 2.3.0b1 Before this Werk, when trying to create a host_tag_group using an id belonging to an aux_tag the endpoint returned a status 500 (Internal Server Error). This Werk fixes that behaviour and now returns a status 400, informing that the id is in use. CMK-15167