feat(dao) add two cassandra migration helpers
feat(dao) add two cassandra migration helpers

* copy_records() to copy column families to auxiliary tables
* add_partition() to add the `partition` primary key component for some
  new DB entities

From #3373

Signed-off-by: Thibault Charbonnier <3c2e9133e272cb489e2fea0c4328cf56b08e4226@me.com>

Kong/kong,Kong/kong,Kong/kong,Mashape/kong