How to using query iterators with new MilvusClient method?

[secsilm]

The current document uses the old way.

[yhmo]

MilvusClient has no interface for iterator. Just use the old way.

[xiaofan-luan]

@czs007 let's add one.
iter:=MilvusClient.open
defer iter.Close()
while iter.hasNext()
process(iter.next())

[czs007]

@secsilm @xiaofan-luan
LGTM
It's on my schedule.