MEP 24 -- Support bulk load

Current state: Accepted

ISSUE: https://github.com/milvus-io/milvus/issues/15604

PRs: 

Keywords: bulk load, import

Released: with Milvus 2.1 

Authors:  

Summary

Import data by a shortcut to get better performance compared with insert(). 

Motivation

Typically, it cost several 5~6 hours to insert one billion entities with 128-dimensional vectors. We need a new interface to do bulk load for the following purposes:

1. copy a collection from one Milvus 2.0 server to another.
2. import data from json format files
3. import data from numpy format files
4. import data from Milvus 1.x to Milvus 2.0

Design Details

SDK Interfaces

RPC Interfaces

Internal machinery

Test Plan