Log DDL statements on coordinator

People sometimes run into issues with schema, and that is often because they do concurrent schema changes, which are just not supported and we should fix that someday, but in the meantime, it's not always easy to even check if you may indeed have had concurrent schema changes.

A very trivial way to make that easier would be to simply log DDL statements on the coordinator before they are executed. This is likely useful info for operators in the first place, and would allow in most case to track if concurrent schema was the likely cause of a particular issue seen.

Additional info for newcomers:

In order to implement this change you will need to modify org.apache.cassandra.cql3.QueryProcessor to log the schema change before it is executed.