feat: add models for gitee.ai

[fchange]

Checklist:

[!IMPORTANT]
Please review the checklist below before submitting your pull request.

• [X] Please open an issue before creating a PR or link to an existing issue
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

This pull request introduces support for Gitee AI as a new model provider.

Close https://github.com/langgenius/dify/issues/9243

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update, included: Dify Document
• [ ] Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• [ ] Dependency upgrade

Testing Instructions

The changes were tested using manually filled credentials.

[fchange]

validate_credentials has been implemented and self-tested.

[crazywoola]

validate_credentials has been implemented and self-tested.

I mean you need to add tests here like this one https://github.com/langgenius/dify/blob/7c0b159a81f099c5089c96ba77b32d592e5787b8/api/tests/integration_tests/model_runtime/openai/test_llm.py

[fchange]

Added tests，because they use the real Gitee AI service, which requires a correctly filled access_token to run successfully. Therefore, the test command was not added to pytest_model_runtime.sh @crazywoola

[bluishoul]

@crazywoola you can sign up Gitee AI, and use the free token(100 requests limit per day) to run the tests: https://ai.gitee.com/dashboard/settings/tokens