[release/8.0-preview3] Fix histogram chart calculation (#1993)

* Fix histogram chart calculation

* Comment

* Update src/Aspire.Dashboard/Components/Controls/ChartContainer.razor.cs

Co-authored-by: Drew Noakes <git@drewnoakes.com>

* Update src/Aspire.Dashboard/Components/Controls/ChartContainer.razor.cs

---------

Co-authored-by: James Newton-King <james@newtonking.com>
Co-authored-by: Drew Noakes <git@drewnoakes.com>

src/Aspire.Dashboard/Components/Controls/ChartContainer.razor.cs

@@ -170,13 +170,18 @@ protected override async Task OnParametersSetAsync()
 
     private OtlpInstrument? GetInstrument()
     {
+        var endDate = DateTime.UtcNow;
+        // Get more data than is being displayed. Histogram graph uses some historical data to calculate bucket counts.
+        // It's ok to get more data than is needed here. An additional date filter is applied when building chart values.
+        var startDate = endDate.Subtract(Duration + TimeSpan.FromSeconds(30));
+
         var instrument = TelemetryRepository.GetInstrument(new GetInstrumentRequest
         {
             ApplicationServiceId = ApplicationId,
             MeterName = MeterName,
             InstrumentName = InstrumentName,
-            StartTime = DateTime.UtcNow.Subtract(Duration),
-            EndTime = DateTime.UtcNow,
+            StartTime = startDate,
+            EndTime = endDate,
         });
 
         if (instrument == null)