--Add support for nested User-defined attributes

[jturner65]

Motivation and Context

Presently, the user-defined attributes fields within the various configuration files only support a single layer of data values of various types, but this PR adds support for nested json objects within user-defined attributes values, enabling a user to be able to specify sub-groupings within these fields.

This functionality is required for ReplicaCAD to be properly used in Habitat 2.0 (to provide support for per-object placement box configurations)

How Has This Been Tested

Tests added in c++ to verify functionality. Tested locally c++ and python

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.