feat(echarts-pie): add string template support for labels (#28774)

superset-frontend/plugins/plugin-chart-echarts/src/Pie/controlPanel.tsx

@@ -123,11 +123,31 @@ const config: ControlPanelConfig = {
                 ['key_percent', t('Category and Percentage')],
                 ['key_value_percent', t('Category, Value and Percentage')],
                 ['value_percent', t('Value and Percentage')],
+                ['template', t('Template')],
               ],
               description: t('What should be shown on the label?'),
             },
           },
         ],
+        [
+          {
+            name: 'label_template',
+            config: {
+              type: 'TextControl',
+              label: t('Label Template'),
+              renderTrigger: true,
+              description: t(
+                'Format data labels. ' +
+                  'Use variables: {name}, {value}, {percent}. ' +
+                  '\\n represents a new line. ' +
+                  'ECharts compatibility:\n' +
+                  '{a} (series), {b} (name), {c} (value), {d} (percentage)',
+              ),
+              visibility: ({ controls }: ControlPanelsContainerProps) =>
+                controls?.label_type?.value === 'template',
+            },
+          },
+        ],
         [
           {
             name: 'number_format',