Execute statements atfer reading each record found by statement

[rigon]

This allows to execute queries that modify data in the database after reading each record.
For example, this allows to update or delete records already imported.

Example to update records:

input {
    jdbc {
        statement => "SELECT id FROM test"
        post_statement => "UPDATE test SET flag = 1 WHERE id = :id"
    }
}

Example to delete records:

input {
    jdbc {
        statement => "SELECT id FROM test"
        post_statement => "DELETE FROM test WHERE id = :id"
    }
}