Optimize `ADD INDEX` Operations in MySQL Sink

[hongyunyan]

Currently, when the sink encounters an ADD INDEX statement, it attempts a synchronous execution. Only after this initial attempt times out (the default is 2 minutes) does the sink transition to the more efficient asynchronous DDL execution mode. This waiting period is an unproductive use of time.

We should change the logic so that the MySQL Sink immediately executes ADD INDEX statements in asynchronous mode, without first waiting for a timeout.