eliminate redundant join when find hashing join condition
such as for plan:
```
T1 join T2 on T1.id = T2.id join T3 on T1.id = T3.id and T2.id = T3.id
```
we infer a new predicate T1.id = T2.id which is redundant. Therefore we need to eliminate it when find hash condition
This PR proposes mapping external catalog JSON types to String instead of JsonB in Apache Doris. This change is motivated by the realization that JDBC retrieves JSON data as a String JSON string, regardless of its storage format (Json(String) or Json(Binary)). Mapping to String streamlines data retrieval, simplifies write-backs, and ensures compatibility with all JSON(String) and JSON(Binary) functions, despite potentially misleading displays of JSON data as Strings in Doris. This approach avoids the performance overhead and complexity of converting each row of data from JsonB to String, making the process more efficient and elegant.
About Upgrade
To ensure query compatibility with existing Catalogs in the upgraded version,we currently still retain the capability to query external JSON types as JSONB. However, once you upgrade to the new version and either refresh the Catalog or create a new one, all external JSON types will be treated as Strings. To ensure consistent behavior,and possible future removal of support for JSON as JSONB query code, it is highly recommended that you manually refresh your Catalog as soon as possible after upgrading to the new version.
2 tests cases (ShowCreateFunctionTest and ShowFunctionTest) have function name clash;
because of which one of the test fails to complete setup() and eventually fail for not able to create funciton.
Changed the name of the test function in 1 of the file.
Meta data place holder for statistics in version 2.1.x. Users could upgrade to this version, but doesn't support rollback.
After this change, statistics related functions doesn't need to change meta data any more in the 2.1 series.
In this PR, we will control whether the external data source query is a push-down function parameter in the filter condition, changing the enable_fun_pushdown of fe conf to the enable_ext_func_pred_pushdown of the variable
