[Docs] Adds Rack Power Utilization

[joewesch]

Closes: DNE

What's Changed

This was originally added in #4184, but it didn't get transferred to the 2.0 docs as the Power Tracking page no longer exists. I figured the Rack documentation page was the next logical place for it, but let me know if you want me to move it somewhere else.

TODO

• Explanation of Change(s)
• Added change log fragment(s) (for more information see the documentation)
• Attached Screenshots, Payload Example
• Unit, Integration Tests
• Documentation Updates (when adding/changing features)
• Example Plugin Updates (when adding/changing features)
• Outline Remaining Work, Constraints from Design

[glennmatthews]

Thank you!