Werk #16137: user_config: allow update of custom user attributes

This werk addresses an issue reported, where you could create a user with custom attributes, but you could not update the user's custom attributes.

E.g.

Calling this endpoint with the following payload would work, providing the custom attribute 'attr_1' exists.

POST check_mk/api/v1/domain-types/user_config/collections/all

{
        "username": "user_1",
        "fullname": "user_1",
        "auth_option": {
            "auth_type": "password",
            "password": "password_with_at_least_12_characters"
        },
        "disable_login": false,
        "contact_options": {
            "email": "user@example.com"
        },
        "pager_address": "",
        "idle_timeout": {"option": "global"},
        "roles": ["user"],
        "authorized_sites": ["heute"],
        "contactgroups": ["all"],
        "disable_notifications": {"disable": false},
        "language": "de",
        "temperature_unit": "celsius",
        "interface_options": {
            "interface_theme": "dark"
        }
        "attr_1": "some_text",
}

However, attempting to modify this user with the edit user endpoint

PUT check_mk/api/v1/objects/user_config/user_1

{
    "attr1": "edited_text"
}

would fail and return a response like so

{
    "title": "Bad Request",
    "status": 400,
    "detail": "These fields have problems: _schema",
    "fields": {
        "_schema": [
            "Unknown Attribute: 'attr_1'"
        ]
    }
}

We now check for custom user attributes on the update endpoint and allow them if they exist, just like the create user endpoint.

To the list of all Werks