feat: credit pool

[zyssyz123]

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Summary

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 make lint and make type-check (backend) and cd web && npx lint-staged (frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @zyssyz123, 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 implements a comprehensive credit pooling system to manage usage for hosted services, enhancing the platform's ability to handle trial and paid quotas for tenants. It also integrates support for new large language model providers and updates existing ones, providing a more flexible and scalable foundation for AI model consumption and billing. The changes ensure that credit usage is accurately tracked and reflected across the system, particularly in cloud environments.

Highlights

• Credit Pooling System: Introduced a new credit pooling system for hosted services, allowing for centralized management of trial and paid credits for tenants. This includes a new database table tenant_credit_pools and a CreditPoolService.
• New Hosted LLM Provider Support: Added configuration and integration for several new hosted LLM providers: Gemini, XAI, Deepseek, and Tongyi, expanding the range of available models.
• Enhanced Quota Management: Updated the quota deduction logic to utilize the new credit pooling system for trial and paid quotas, ensuring accurate tracking and consumption of credits across different models and providers.
• Expanded OpenAI Model List: Significantly expanded the list of supported OpenAI trial models, including various GPT-4, GPT-3.5, and upcoming GPT-4o and GPT-5 series models.
• Workspace Information Enrichment: The workspace tenant information now includes details about trial_credits, trial_credits_used, and next_credit_reset_date for cloud deployments, providing better visibility into credit usage.

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[gemini-code-assist]

Code Review

This pull request introduces a credit pool system for managing usage of hosted services, which is a significant and positive architectural change. The implementation is mostly solid, but I've identified a few critical issues, particularly a race condition in the credit deduction logic that could lead to incorrect billing. I've also found several minor copy-paste errors and typos. Addressing these points will improve the robustness and maintainability of this new feature.

[hj24]

LGTM