MySQL 5.x: enums are strings during snapshot, integers during CDC

[ilidemi]

In 8.x we enforce binlog_row_metadata=full that gives us strings on both paths. 5.x doesn't support full so snapshot gets strings and CDC gets integers that we can't easily resolve. For consistency, snapshot 5.x enums as integers.

Repro on 5.7:

CREATE TABLE with_enum (
    id INT AUTO_INCREMENT PRIMARY KEY,
    status ENUM('active', 'inactive', 'pending') NOT NULL
);

INSERT INTO with_enum (status) values ('active');

-- (do snapshot)

INSERT INTO with_enum (status) values ('active');

After the CDC batch goes through, one row will have status='active' and the other status='1'.