This method is used to create collection
use to provide collection information to be created.
Get collection detail, like name ,schema
Drop collection, also will drop all datas in this collection.
Will return collection statistics.
Only row_count for now.
Check collection exist or not
Befor search need load collection to cache.
If you want to reduce your cache usage, you can release some collections.
But you cant search in unload collections.
List all collections