Modify response of DescribeCollection and add DescribePartition

[czs007]

After the client LoadCollection/LoadPartition, there needs to be a way to know if the Collection/Partition is loaded. Previously, it relied on the ShowCollections/ShowPartitions interface to obtain whether it was loaded into memory. Based on RBAC requirements , the dependency on ShowCollections should be removed and resort to use the DescribeCollection/DescribePartition.
Client which can perform Load operattion on Partition/Collection should also has the priviliege to execute DescribeCollection/DescribePartition .