[query agent] Allow to execute DML statements

[eolivelli]

Summary:

• in the "query" / "query-vector-db" agents you can now set "mode=execute"
• you can also configure a list of "generated keys" columns, returned by the database (for instance of you insert a record and you want to get the value for the PK automatically assigned)
• then you can execute DML queries
• in this case the results depend on the Database implementation
• for JDBC datasource in the output field the agent puts a Map with the update count and the generated keys