Consider adding multi-target cluster 'AutoQueueSwitch'

WsSQL jobs targeting a thor cluster potentially block subsequent requests. We can mitigate the queuing by adding support for user specified #OPTION('allowedClusters ',<>), and enabling 'AllowAutoQueueSwitch'.

If multiple thor based target clusters exists, the query execution could be switched to an available cluster.

The execute and executePrepared methods already provide a target cluster field. The field will now accept a comma delimited list, which after validation, would be added to the #OPTION('allowedClusters ',<>) command.

jamesdefabiarichardkchapman comments/concerns?