Detailed TD calibration step test for HueForge by @XavierFaraudo

No changes from original design.I report original description:UPDATED 2023-07-25: Added a guide on how to use this test, plus other additional info. If you're interested just in using the test, don't read it whole; just read the “What is the Blending Distance (BD)?” section and do the steps of testing, but skip all "Additional Info" and "Advanced uses" sections.On 2023-06-27, Steve from HueForge introduced the new “step test” calibration for the all-important TD in HueForge. This may replace the