docs: update pivot corner option

Author: fangsmile

docs/assets/option/en/common/pivot-corner.md

@@ -33,3 +33,6 @@ Header cell style, the configuration items vary slightly depending on the header
 - For headerType 'text', refer to [headerStyle](../option/PivotTable-columns-text#headerStyle.bgColor)
 - For headerType 'link', refer to [headerStyle](../option/PivotTable-columns-link#headerStyle.bgColor)
 - For headerType 'image', refer to [headerStyle](../option/PivotTable-columns-image#headerStyle.bgColor)
+
+ ${prefix} forceShowHeader(boolean)
+ Force display of corner header. When there are no dimensions in the row or column direction, the corner header will not be displayed by default. However, in some scenarios, it is still necessary to display the dimension name in the corner header, please configure this field.

docs/assets/option/zh/common/pivot-corner.md

@@ -33,3 +33,6 @@ ${prefix} headerStyle(TODO)
 - headerType 为'text'，对应[headerStyle](../option/PivotTable-columns-text#headerStyle.bgColor)
 - headerType 为'link'，对应[headerStyle](../option/PivotTable-columns-link#headerStyle.bgColor)
 - headerType 为'image'，对应[headerStyle](../option/PivotTable-columns-image#headerStyle.bgColor)
+
+ ${prefix} forceShowHeader(boolean)
+ 强制显示角头。当row或者column方向上没有维度的时候 本身是不会显示角表头的 但是某些场景下仍然需显示维度名称在角头，请配置这个字段。