Clarify guidance around ids in arrays

[mrshll1001]

Based off of CRM-7304.

The schema style guide states that every object within an array should have an id field to support merging and flattening.

However we've given advice to the contrary ie when determining that an id field was not preferred in an implementation of the links extension. The reasoning was it made more sense for the links to be interpreted in the context of individual releases and for those links to be dropped from the compiled release.

The handbook should ideally reflect this logic to make it clearer where cases exist that make more sense not to include an id in objects that exist in arrays.