Added Enum Data Type as a Synonim for Enum8 or Enum16

Why it matters

This feature simplifies the usage of enum types in ClickHouse by allowing users to use the generic Enum keyword without specifying the underlying size explicitly. It enhances usability and compatibility by abstracting away complexity related to choosing between Enum8 and Enum16.

How to use it

Users can now declare enum columns using Enum instead of Enum8 or Enum16. For example:

CREATE TABLE example (
  status Enum('active' = 1, 'inactive' = 2)
) ENGINE = ...

The system will internally choose the appropriate enum size.