Ability to have multiple collections for a single model

[lklic]

Rather than have a model mapped to a milvus collection, I think it would be good to be able to use a single model and store the data in multiple collections. This can be useful to isolate certain collections of images, where one would want to query only those. For example we could have images of rectos and versos for photographs, or add separate milvus collections for museum images that we may want to search across.