The deprecated message is now attached to a new attribute returned with
the results. This message can then be read by clients to warn a user
about upcoming changes to the query engine.
The `influx` client has already been modified to read this message and
print it out for every format except CSV.
The first warning message is a deprecated message about removing `IF NOT
EXISTS` from `CREATE DATABASE`.
The message will also be printed to the server log.
Fixes#5707.