docs: add the DECIMAL property data type

content/cn/docs/clients/hugegraph-client.md

@@ -120,6 +120,7 @@ PropertyKey 允许定义的约束信息包括：name、datatype、cardinality、
 | asByte()    | Byte       |
 | asBlob()    | Byte[]     |
 | asDouble()  | Double     |
+| asDecimal() | BigDecimal（精确十进制；不可索引，不可作主键/排序键；自包含 apache/hugegraph#3209 与 #771 的版本起可用） |
 | asFloat()   | Float      |
 | asLong()    | Long       |
 

content/cn/docs/clients/restful-api/propertykey.md

@@ -10,7 +10,7 @@ description: "PropertyKey（属性键）REST 接口:定义图中所有属性的
 Params 说明：
 
 - name：属性类型名称，必填
-- data_type：属性类型数据类型，包括：bool、byte、int、long、float、double、text、date、uuid、blob，默认 `text` 类型 (代表 string 字符串类型)
+- data_type：属性类型数据类型，包括：bool、byte、int、long、float、double、decimal、text、date、uuid、blob，默认 `text` 类型 (代表 string 字符串类型)。`decimal` 为精确十进制数 (Java `BigDecimal`)：最多 128 位有效数字，小数位数 (scale) 绝对值不超过 128；请求中可以用 JSON 数字或字符串传入，两种形式都会被精确读取；响应中以字符串返回（例如 `"amount": "12345678901234567890.123456789012345678"`），客户端应使用 `new BigDecimal(String)` 解析，不要按 double 解析。decimal 属性不能建索引，不能作为主键或边的排序键，也不能设置 OLAP 索引类的 write type（仅支持 `OLAP_COMMON`）。自包含 apache/hugegraph#3209 与 apache/hugegraph-toolchain#771 的版本起可用
 - cardinality：属性类型基数，包括：single、list、set，默认 `single` (代表单属性值)
 
 请求体字段说明：

content/en/docs/clients/hugegraph-client.md

@@ -119,6 +119,7 @@ The constraint information that PropertyKey allows to define includes: name, dat
 | asByte()    | Byte       |
 | asBlob()    | Byte[]     |
 | asDouble()  | Double     |
+| asDecimal() | BigDecimal (exact decimal, not indexable, not a primary/sort key; from the release with apache/hugegraph#3209 and #771) |
 | asFloat()   | Float      |
 | asLong()    | Long       |
 

content/en/docs/clients/restful-api/propertykey.md

@@ -10,7 +10,7 @@ description: "PropertyKey REST API: Define data types and cardinality constraint
 Params Description:
 
 - name: The name of the property type, required.
-- data_type: The data type of the property type, including: bool, byte, int, long, float, double, text, blob, date, uuid. The default data type is `text` (Represent a `string` type)
+- data_type: The data type of the property type, including: bool, byte, int, long, float, double, decimal, text, blob, date, uuid. The default data type is `text` (Represent a `string` type). `decimal` holds an exact decimal number (Java `BigDecimal`): at most 128 significant digits and a scale of at most 128 in either direction; in a request it may be sent as a JSON number or as a string and is read exactly either way; in a response it is returned as a string (e.g. `"amount": "12345678901234567890.123456789012345678"`), so a client parses it with `new BigDecimal(String)`, never as a double. A decimal key cannot be indexed, used as a primary key or an edge sort key, or given an OLAP index write type (only `OLAP_COMMON`). Available from the release that ships apache/hugegraph#3209 and apache/hugegraph-toolchain#771
 - cardinality: The cardinality of the property type, including: single, list, set. The default cardinality is `single`.
 
 Request Body Field Description: