docs: Indented layoutCfg.indent support function (#3109)

* docs: Indented layoutCfg.indent support function

We can set node's horizontal offset dynamically with function,
which allow user to create custom layout.

Closes #3081

* docs: Indented layoutCfg.indent support function

Co-authored-by: powellpeng <powellpeng@tencent.com>

packages/site/docs/api/treeGraphLayout/indented.en.md

@@ -23,7 +23,17 @@ Indented layout represents the hierarchy by indent between them. Each node will
 
 ### layoutCfg.indent
 
-**Type**: Number<br />**Default**: 20<br />**Required**: false<br />**Description**: Colunm separation
+**Type**: Number | Function<br />**Default**: 20<br />**Example**：
+
+```javascript
+(d) => {
+  // d is a node
+  if (d.parent?.id === 'testId') return d.parent.x + 50;
+  return 100;
+};
+```
+
+**Required**: false<br />**Description**: When the type is Number, the colunm separation is a fixed value; When the type is Function, the distance between the node and the root node is the returned value of the function.
 
 ### layoutCfg.getWidth
 

packages/site/docs/api/treeGraphLayout/indented.zh.md

@@ -23,7 +23,17 @@ order: 3
 
 ### layoutCfg.indent
 
-**类型**：Number<br />**默认值**：20<br />**是否必须**：false<br />**说明**：列间间距
+**类型**：Number | Function<br />**默认值**：20<br />**示例**：
+
+```javascript
+(d) => {
+  // d 是一个节点
+  if (d.parent?.id === 'testId') return d.parent.x + 50;
+  return 100;
+};
+```
+
+**是否必须**：false<br />**说明**：类型为Number时，列间间距是固定值；类型为Function时，节点与根结点的间距是函数返回值。
 
 ### layoutCfg.getWidth