[Improvement] Gravitino REST will be compatible with unstructured data or not

### What would you like to be improved?

Like create table SQL, some user using unstructured data to create table with complex column, instead of JOSN provided by Gravitino.

Gravitino REST will be compatible with unstructured data or not? This may be a consideration between user usability and system standardization

CREATE TABLE `test.onemeta_test_table_61` (
`string_type` STRING comment "string类型"
`address` STRUCT, state: BIGINT, zip: STRING>>, state: BIGINT, zip: STRING> comment "自定义嵌套"
) COMMENT 'test'
PARTITIONED BY (
log_date STRING comment "String分区",
) ;

### How should we improve?

1. When we introduce Gravitino, we package Gravitino REST interface to provide better usability for our own users

2. Gravitino considers introducing a parser to parse unstructured data transmitted by users, which may have a bad impact on the standardization of the system

Start by reviewing the Gravitino REST interface and the supplied CREATE TABLE example, focusing on how complex nested columns are represented. Determine whether unstructured SQL-like input is in scope or whether standardized JSON remains required, then document the decided behavior and its validation criteria.

Written by the indexing model from the issue text.