Use some better HTML/Markdown format structure to show which query response fields are optional

[thadguidry]

In the 4.1 section for Query Structures, we say easily that query and properties are required and all other fields are optional.
But in 4.2 section for Query Responses, we have the optional properties within the field description sentences and it's hard to quickly see what is optional or not. Maybe some formatting changes like bold, paratheses, or something to make it easier for developers to quickly scan and read which fields are optional or not.