To support xgboost and ant-xgboost in SQLFlow

[Yancey0623]

Is your feature request related to a problem? Please describe.
We prefer to support ant-xgboost and xgboost in SQLFlow, we can keep the SQL syntax consistent and distinguish the difference xgboost branch with env SQLFLOW_WITH_ANTXGBOOST=ON,

• rename code from the exsiting xgboost to ant-xgboost rename xgboost to ant_xgboost #754
• Refine Dockerfile to install xgboost or ant-xgboost by build arg SQLFLOW_WITH_ANTXGBOOST
• Enable test ant-xgboost and xgboost on CI system.

[typhoonzero]

XGBoost support is already implemented in previous commits.