Add the ability to order tables that are not required in the instance/solution schema

I am missing functionality to assign an order to all instance/solution tables. Currently, tables can be ordered using the required property in the JSON schema. However, if a table is optional, there is no way to include it in that order.

Start by tracing how the instance/solution JSON schema's required property is read and how table order is produced in the REST API. Define how an explicit order should include optional tables, then verify that required-table ordering remains unchanged and that optional tables follow the requested order.

Written by the indexing model from the issue text.