[ML] Data drift: Code Consolidation

[qn895]

For the refactor of Data drift chart, some code was copied over and modified from the DocumentCountChart with Dual Brush. This issue tracks progress on consolidating the copied code into shared utilities.

• Add comments to duplicated UI code
  [ML] Improves Data drift time range selection & show hints for analysis process #174049

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• DocumentCountChartWithBrush → Consolidate with similar component DocumentCountChart in x-pack/packages/ml/aiops_components/src/document_count_chart/document_count_chart.tsx

• SingleBrush → Consolidate with similar component DualBrush in x-pack/packages/ml/aiops_components/src/dual_brush/dual_brush.tsx

[elasticmachine]

Pinging @elastic/ml-ui (:ml)