add llm: ernie-character-8k of wenxin

[jiaqianjing]

Description

add support about ernie-character-8k of wenxin. It is very good at human-like conversation in chat scenarios.

Fixes # (issue)

Type of Change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement

Suggested Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods
• [ ] optional I have made corresponding changes to the documentation
• [ ] optional I have added tests that prove my fix is effective or that my feature works
• [ ] optional New and existing unit tests pass locally with my changes