object_type documentation and values

[endorama]

While working on elastic/integrations#4004 a question emerged around object_type valid values.

This field is documented in a confusing way in package spec:

package-spec/spec/integration/data_stream/fields/fields.spec.yml

Lines 235 to 238 in c8a0fe0

	object_type:
	description: >
	Required for `type: array` to specify the data type in the array.
	type: string

After #412, that removed type: array, I think the description is misleading and leaves a lot of questions unanswered around when and how to use object_type.

Any clarification on this would be greatly appreciated!