Fix Chat Completion Stream API and Swagger Docs

[GirinMan]

Feature request

• This issue encompasses two distinct improvements: fixing the Chat Completion Stream API to align with official OpenAI API behavior, and enhancing the Swagger Docs for better usability and clarity.
• Specifically, the Stream API fix involves ensuring the final chunk in a stream correctly returns as an empty object rather than erroneously containing null "role" and "content".
• The Swagger Docs improvement focuses on making the OpenAI compatible API visible, better tagging differentiation, and adding missing schemas to eliminate errors.

Motivation

• The Chat Completion Stream API currently behaves differently from the official OpenAI API in its handling of the final chunk, leading to potential issues for clients expecting OpenAI-compatible behavior.
• This discrepancy can cause unexpected errors and complicates integration efforts.
• Additionally, the current state of the Swagger Docs makes it challenging for users to navigate and understand the available API features and capabilities.
• Enhancing these aspects of the project will improve its compatibility, usability, and overall user experience.

Your contribution

• I plan to address these issues by submitting a PR that implements the necessary fixes and improvements.
• This will include code adjustments for the Chat Completion Stream API, as well as updates to the Swagger Docs to address the identified shortcomings.