Add support for polar charts

- As per [documentation](https://www.highcharts.com/docs/chart-and-series-types/polar-chart):

> Polar charts, also known as radar charts, require the highcharts-more.js file.

I was also tinkering with the idea to just merge the if to the "waterfall" case below as it's essentially the same, but then decided against as it might cause issues in the future.

ember-highcharts/src/components/high-charts.ts

@@ -256,6 +256,11 @@ export default class HighCharts<
       SolidGauge.default(Highcharts);
     }
 
+    if (this.args.chartOptions?.chart?.polar === true) {
+      const More = await waitForPromise(import('highcharts/highcharts-more'));
+      More.default(Highcharts);
+    }
+
     if (this.args.chartOptions?.chart?.type === 'waterfall') {
       const More = await waitForPromise(import('highcharts/highcharts-more'));
       More.default(Highcharts);