[ML] APM Correlations: Round duration values to be used in range aggr…

…egations. (elastic#114833)

A change in the ES range agg no longer accepts numbers with decimals if the underlying field is typed as long. This fixes the issue by rounding the values we pass on to the range agg.

x-pack/plugins/apm/server/lib/search_strategies/queries/query_histogram_range_steps.test.ts

@@ -106,8 +106,8 @@ describe('query_histogram_range_steps', () => {
       );
 
       expect(resp.length).toEqual(100);
-      expect(resp[0]).toEqual(9.260965422132594);
-      expect(resp[99]).toEqual(18521.930844265193);
+      expect(resp[0]).toEqual(9);
+      expect(resp[99]).toEqual(18522);
       expect(esClientSearchMock).toHaveBeenCalledTimes(1);
     });
   });

x-pack/plugins/apm/server/lib/search_strategies/queries/query_histogram_range_steps.ts

@@ -19,10 +19,11 @@ import { getRequestBase } from './get_request_base';
 
 const getHistogramRangeSteps = (min: number, max: number, steps: number) => {
   // A d3 based scale function as a helper to get equally distributed bins on a log scale.
+  // We round the final values because the ES range agg we use won't accept numbers with decimals for `transaction.duration.us`.
   const logFn = scaleLog().domain([min, max]).range([1, steps]);
   return [...Array(steps).keys()]
     .map(logFn.invert)
-    .map((d) => (isNaN(d) ? 0 : d));
+    .map((d) => (isNaN(d) ? 0 : Math.round(d)));
 };
 
 export const getHistogramIntervalRequest = (