[ML] Explain Log Rate Spikes: Fix wide time range display with sparse data. (#147129)

The `date_histogram` query was updated to use `min_doc_count: 0` and set
`extended_bounds` to the date pickers time range so it returns buckets
for all necessary time slots necessary for the full date histogram bar
chart.

x-pack/plugins/aiops/public/components/document_count_content/document_count_content/document_count_content.tsx

@@ -12,9 +12,10 @@ import { EuiButtonEmpty, EuiFlexGroup, EuiFlexItem } from '@elastic/eui';
 import { i18n } from '@kbn/i18n';
 import type { WindowParameters } from '@kbn/aiops-utils';
 
+import { DocumentCountStats } from '../../../get_document_stats';
+
 import { DocumentCountChart, DocumentCountChartPoint } from '../document_count_chart';
 import { TotalCountHeader } from '../total_count_header';
-import { DocumentCountStats } from '../../../get_document_stats';
 
 const clearSelectionLabel = i18n.translate(
   'xpack.aiops.documentCountContent.clearSelectionAriaLabel',

x-pack/plugins/aiops/public/components/explain_log_rate_spikes/explain_log_rate_spikes_page.tsx

@@ -97,7 +97,7 @@ export const ExplainLogRateSpikesPage: FC<ExplainLogRateSpikesPageProps> = ({
       queryLanguage: SearchQueryLanguage;
       filters: Filter[];
     }) => {
-      // When the user loads saved search and then clear or modify the query
+      // When the user loads a saved search and then clears or modifies the query
       // we should remove the saved search and replace it with the index pattern id
       if (currentSavedSearch !== null) {
         setCurrentSavedSearch(null);

x-pack/plugins/aiops/public/get_document_stats.ts

@@ -71,7 +71,11 @@ export const getDocumentCountStatsRequest = (params: DocumentStatsSearchStrategy
       date_histogram: {
         field: timeFieldName,
         fixed_interval: `${intervalMs}ms`,
-        min_doc_count: 1,
+        min_doc_count: 0,
+        extended_bounds: {
+          min: earliestMs,
+          max: latestMs,
+        },
       },
     },
   };