Werk #14534: Add unit conversion support for graphs

Note: This werk is deprecated in favor of werk 15660. As of werk 15660, unit conversions are no longer configurable via graph tunings. Any already exisiting settings will be ignored (all configurable conversions were anyway conversions between temperature units).

This werk adds the support for converting the displayed unit of a metric in a graph.

Currently we only support conversion of degrees from Celsius to Fahrenheit or Kelvin but this can be extended in the future.

To convert a unit you can use the Convert unit to option in Graph Tunings.

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