[FEATURE] add support for schema to better support attribute groups?

[JoernBerkefeld]

it seems attribute groups are listed under schemas? and then there they can be selected by key? see this link for details: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/retrieveAttributeGroupsID.html?q=attributeGroup

maybe we need to restructure this type similar to campaign & campaign assets? FYI @DougMidgley