Werk #13651: API: fix user config show endpoints to include user attributes

In the previous version, both the show user and show all users endpoints did not behave as intended hiding the user attributes. This werk changes this behaviour and also introduces proper field definitions for the response schema. The response of the user endpoint has also changed. Every attribute which was previously returned under "extensions.attributes", will now be returned directly under "extensions". You may have to change your scripts accordingly. The affected endpoints are:

*/objects/user_config/user (get & put) */domain-types/user_config/collections/all (get & post)

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