feat(transform): Add UtilityControl Transform for Generating Ctrl Messages

[jshlbrd]

Description

• Adds the utility_control transform for generating control (ctrl) messages
• Updates aggregate transforms to skip empty results

Motivation and Context

This provides an option to manage how data flows through the system, which is otherwise impossible without creating or modifying the application code. Triggering ctrl messages is based on the amount of data passed through the system, which relies on the commonly used batching / aggregation methods.

This also fixes a bug where some aggregate transforms can create empty results.

How Has This Been Tested?

Added an example for the new transform.

Types of changes

• 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.