@Override
    public String toString() {
        return username + '@' + host + ':' + port;
    }
The connection pool identifier.
Copy from com.ververica:flink-cdc-base:2.3.0.
inlong-sort/sort-flink/cdc-base/src/main/java/org/apache/inlong/sort/cdc/base/relational/connection/ConnectionPoolId.java