feat: support json_schema for ollama models

[hjlarry]

Summary

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Close issue syntax: Fixes #<issue number> or Resolves #<issue number>, see documentation for more details.

offical doc https://ollama.com/blog/structured-outputs

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• 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

[bowenliang123]

Good job, my thumbs up for it !
Could you add this feature for OpenAI-compatible providers as well ?

[hjlarry]

Good job, my thumbs up for it ! Could you add this feature for OpenAI-compatible providers as well ?

sure! Is there any model for test this feature?

[bowenliang123]

Two approaches in mind:

• use ollama's endpoint in OpenAI compatible provider with Qwen 2.5 models
• use SiliconFlow's models in OpenAI compatible provider

[hjlarry]

I check the SiliconFlow's doc https://docs.siliconflow.cn/guides/json-mode
seems it only support json_object , not support json_schema ?