Force heatmap y-axis to be category type (opensearch-project#167)

Signed-off-by: Tyler Ohlsen <ohltyler@amazon.com>

Author: ohltyler

public/pages/AnomalyCharts/containers/AnomalyHeatmapChart.tsx

@@ -633,6 +633,7 @@ export const AnomalyHeatmapChart = React.memo(
                       showgrid: false,
                       fixedrange: true,
                       automargin: true,
+                      type: 'category',
                       tickmode: 'array',
                       tickvals: heatmapData[0].y,
                       ticktext: heatmapData[0].y.map((label: string) =>