Please add support for atomic swapping for Collections in SolrCloud

Similar to the concept of swapping regular Solr cores online, I'd like to request support for atomic swapping of entire Collections in SolrCloud.

This would aid in online schema changes, online sharding changes, etc. Ideally the new collection would be in sync with the current when swapped.

At a high level, I believe this could be achieved if replicas of CollectionA could be brought up in CollectionB, then swapped atomically when in sync. I imagine a momentary pause to updates would need to occur, which would be acceptable for at least my use cases.

Currently I can create a new collection under a new collection name and swap paths in the application or rename the core, but this is not elegant/ideal.

Thanks for everyone's hard work on Solr! Great software.

Tim Vaillancourt