feat: start node support json schema

[fatelei]

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Summary

resolve #29052, start node support json

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @fatelei, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the flexibility and robustness of workflow inputs by enabling the 'start node' to accept and validate JSON objects. This feature allows users to define structured data inputs for their workflows, which are then automatically validated against a specified JSON Schema, improving data quality and reducing potential errors at the workflow's entry point.

Highlights

• JSON Object Input Support: The 'start node' in the workflow system now supports a new input type, JSON_OBJECT, allowing structured JSON data to be passed as user input.
• JSON Schema Validation: Inputs of type JSON_OBJECT can now be validated against an optional JSON Schema, ensuring data integrity and adherence to predefined structures. This includes checks for required fields, proper JSON formatting, and schema compliance.
• Dependency Addition: The jsonschema library has been added as a new dependency to enable the JSON Schema validation functionality.
• New Test Coverage: A new unit test file has been introduced to specifically verify the correct behavior of JSON object input validation with schemas in the start node.

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[gemini-code-assist]

Code Review

This pull request adds support for JSON object variables in the start node, including validation against a JSON schema. The changes in the backend are well-structured, introducing a new JSON_OBJECT variable type and implementing the validation logic in the StartNode. The addition of a new dependency jsonschema is appropriate.

My review focuses on improving the code clarity and test coverage. I've suggested refactoring a small part of the validation logic to remove unreachable code and translating Chinese comments to English for consistency. Most importantly, I've recommended adding more comprehensive test cases to cover various edge cases and error scenarios, which will make the new feature more robust.

Overall, this is a good feature addition. Addressing the feedback will improve the quality and maintainability of the code.

[QuantumGhost]

This also requires updating to documentation.

Other changes LGTM.