fix(dao) assume C* > 3.x will use the same system schema

To ensure that Kong works with DataStax DSE 6.0 (which uses Cassandra
4.x), we can for now assume that the system schema will be identical as
that of Cassandra 3.x.

This does NOT mean Kong is compatible with Cassandra 4.x, and is only
meant as a temporary hotfix for users wishing to run/test Kong with
advanced versions of Cassandra.

Fix #3410

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

Author: mprimeaux

kong/dao/db/cassandra.lua

@@ -697,7 +697,10 @@ function _M:current_migrations()
     end
   end
 
-  if self.major_version_n == 3 then
+  -- For now we will assume that a release version number of 3 and greater
+  -- will use the same schema. This is recognized as a hotfix and will be
+  -- revisited for a more considered solution at a later time.
+  if self.major_version_n >= 3 then
     q_keyspace_exists = [[
       SELECT * FROM system_schema.keyspaces
       WHERE keyspace_name = ?