main-cleanup-PixelConditionsAlgorithms

Implement proposal 27 of ATLASRECTS-7721: Default temperature is only ever set to -7 for pixels. Move this default value to a property on PixelDCSCondTempAlg so that PixelModuleData does not need to be retrieved and interrogated there. The property is nly used in the absence of a sensible reading from the DCS conditions database.