fix:default setting prompt with history messages

[Aries-ckt]

Close #1116

Description

• BufferedConversationMapperOperator
  
• Milvus add username and password

How Has This Been Tested?

when chat knowledge,
default setting prompt should with no history messages

Snapshots:

Include snapshots for easier review.

Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[fangyinc]

r+.

[csunny]

r+