Add missing fuction in services file

Author: georgweiss

core/formula/src/main/resources/META-INF/services/org.csstudio.apputil.formula.spi.FormulaFunction

@@ -49,6 +49,7 @@ org.csstudio.apputil.formula.string.StringEqualsFunction
 org.csstudio.apputil.formula.array.ScaleArrayFormulaFunction
 org.csstudio.apputil.formula.array.SubArrayFunction
 org.csstudio.apputil.formula.array.ElementAtNumberFunction
+org.csstudio.apputil.formula.array.HistogramOfFunction
 org.csstudio.apputil.formula.array.ArraySumFunction
 org.csstudio.apputil.formula.array.ArrayPowFunction
 org.csstudio.apputil.formula.array.ArrayMultiplicationFunction