add MiniMax model client

[mxsl-gr]

trafficstars

Hi, this PR is add MiniMax model client and has passed unit testing. I can provide my api_key if needed for testing

the PR content:

• MiniMax chat client and function calls (not yet supported to return multiple function calls at once)
• MiniMax embedding client
• spring starter
• unit test
• chat client documents
• embedding client documents

MiniMax is a popular LLM in China Mainland recently, the link: MiniMax

For some reasons, products from OpenAI and others can't be directly used in Chinese Mainland.

However ZhiPuAI, Moonshot, MiniMax, BaiChuanAI are referred to as the Four Dragons of China's LLM.

If they can supported, it will further aid spring-ai to promotion in Chinese Mainland.

If necessary, I can take care of subsequent maintenance since I'm currently using them.

The Moonshot PR is #596 The ZhiPuAI PR is #623

I'll also provide PR for BaiChuan later.