Improve Metadata Mediator Testing

[jturner65]

Motivation and Context

This PR expands the MM tests while making them more efficient and faster. It also specifically tests glob file wildcard loading from scene dataset configuration files.

How Has This Been Tested

All existing c++ and python tests pass

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.