Support Partition key

[xige-16]

use case:

from pymilvus import CollectionSchema, FieldSchema, DataType

book_id = FieldSchema(name="book_id", dtype=DataType.INT64, is_primary=True)

book_name = FieldSchema(name="book_name", dtype=DataType.VARCHAR, max_length=200, is_partition_key=true)

book_intro = FieldSchema(name="book_intro", dtype=DataType.FLOAT_VECTOR, dim=2)

default_schema = CollectionSchema(fields=[book_id, book_name, book_intro],description="Test book search")

collection = Collection(name="hello_milvus", schema=default_schema, shards_num=1, partitions=100)

[longjiquan]

/lgtm

[longjiquan]

/approve

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[longjiquan]

cherry-pick of #1425