Gauge - add differential mode

### Description

Add a differential mode, similar option exist for node-red-contrib-ui-artless-gauge

"Option to turn on differential mode. With this option selected, the colored track has center point from which the value is shown. Value of center point can be adjusted. If center value is not defined, the center point is exactly between configured min and max."

### Have you provided an initial effort estimate for this issue?

I can not provide an initial effort estimate

The issue provides no file, test, or entry point. Start by locating the existing Gauge implementation and its min/max handling, then compare the requested behavior with node-red-contrib-ui-artless-gauge. Done means differential mode can be enabled, supports an adjusted center value, and defaults to the midpoint when no center is defined.

Written by the indexing model from the issue text.