Added aggregateBy() function with aggregation type as parameter.

src/datasource-zabbix/metricFunctions.js

@@ -73,6 +73,16 @@ addFuncDef({
   defaultParams: ['1m'],
 });
 
+addFuncDef({
+  name: 'aggregateBy',
+  category: 'Aggregate',
+  params: [
+    { name: 'interval', type: 'string' },
+    { name: 'function', type: 'string', options: ['avg', 'min', 'max', 'median'] }
+  ],
+  defaultParams: ['1m', 'avg'],
+});
+
 addFuncDef({
   name: 'trendValue',
   category: 'Trends',