feat: add discord OpenAPI schema

[Wendong-Fan]

Description

add discord OpenAPI json schema

since we have https://github.com/camel-ai/camel/pull/578 contributed by @yiyiyi0817 and https://github.com/camel-ai/camel/pull/605 contributed by @rsrbk , this PR only need to include OpenAPI json schema part

Motivation and Context

close #545

• [x] I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

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• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds core functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (update in the documentation)
• [ ] Example (update in the folder of example)

Implemented Tasks

• [ ] Subtask 1
• [ ] Subtask 2
• [ ] Subtask 3

Checklist

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• [ ] I have read the CONTRIBUTION guide. (required)
• [ ] My change requires a change to the documentation.
• [ ] I have updated the tests accordingly. (required for a bug fix or a new feature)
• [ ] I have updated the documentation accordingly.