fix(chart): Time Series set showMaxLabel as null for time xAxis (#20627)

* Time Series Chart:

-Apache echarts has this option as false by default for time axis, so we need to override it for our charts so it's uto determined and not fixed to hidden.
- Add AxisType enum so we stop comparing agains raw strings when checking xAxis type

* Time Series Chart:

- set the showMaxLabel option directly without using merge

* Time Series Chart:

 - Rename the property to showMaxLabel as it was originally

superset-frontend/plugins/plugin-chart-echarts/src/Timeseries/transformProps.ts

@@ -41,6 +41,7 @@ import {
   EchartsTimeseriesSeriesType,
   TimeseriesChartTransformedProps,
   OrientationType,
+  AxisType,
 } from './types';
 import { DEFAULT_FORM_DATA } from './constants';
 import { ForecastSeriesEnum, ForecastValue } from '../types';
@@ -337,13 +338,23 @@ export default function transformProps(
       rotate: xAxisLabelRotation,
     },
     minInterval:
-      xAxisType === 'time' && timeGrainSqla
+      xAxisType === AxisType.time && timeGrainSqla
         ? TIMEGRAIN_TO_TIMESTAMP[timeGrainSqla]
         : 0,
   };
+
+  if (xAxisType === AxisType.time) {
+    /**
+     * Overriding default behavior (false) for time axis regardless of the granilarity.
+     * Not including this in the initial declaration above so if echarts changes the default
+     * behavior for other axist types we won't unintentionally override it
+     */
+    xAxis.axisLabel.showMaxLabel = null;
+  }
+
   let yAxis: any = {
     ...defaultYAxis,
-    type: logAxis ? 'log' : 'value',
+    type: logAxis ? AxisType.log : AxisType.value,
     min,
     max,
     minorTick: { show: true },

superset-frontend/plugins/plugin-chart-echarts/src/Timeseries/types.ts

@@ -94,3 +94,10 @@ export interface EchartsTimeseriesChartProps
 
 export type TimeseriesChartTransformedProps =
   EChartTransformedProps<EchartsTimeseriesFormData>;
+
+export enum AxisType {
+  category = 'category',
+  value = 'value',
+  time = 'time',
+  log = 'log',
+}