Users preferences collection schema

Schema to validate collection users preferences schema

type	object
properties
type	type	string
properties	type	object
	properties
	username	type	object
		properties
		type	type	string
	attributes	type	object
		properties
		type	type	string
		items	type	object
			properties
			type	type	string
			properties	type	object
				properties
				key	type	object
					properties
					type	type	string
				value	type	object
					properties
					type	type	string
				user	type	object
					properties
					type	type	string
				timestamp	type	object
					properties
					type	type	string