Enable feature problem

[wyxxxcat]

Previously, the enable feature operation in the upstream would be forwarded to the downstream as the add column operation. We have fixed this problem in apache/doris#46620. In order to be compatible with the whole version, this problem still needs to be handled in CCR.

The current problem is

1. How to identify the enable feature operation and then transform the add column sql

2. How to handle the situation when alter supports multiple operations mixed

alter table t add column k1 int, enable feature "UPDATE_FLEXIBLE_COLUMNS"