[v14] Add missing alias and id to usergroup related api models

[Migaroez]

Prerequisites

• I have added steps to test this contribution in the description below

Description

• Added alias to the usergroup create/update request models to specify the alias of usergroup
• Added alias to the usergroup response/item models to read the alias
• Added an optional id to the usergroup createmodel to specify the id of the newly created usergroup
• refactored some duplicate code, namespacecleanup, ...

Testing

Check whether specifying/updating a usergroup alias trough the post/put endpoints is reflected in all get endpoints
Check whether specifying the id is reflected in the get endpoints
Check whether leaving the id blank in the post results in an id being assigned

[kjac]

Looks good. Tests out good too 👍