feat: optimize for migration versions

[longbingljw]

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Summary

I want to simplify the modification of migration version files when adapting to MySQL.In the past, when I adapted the code for MySQL, I used conditional statements to ensure the PostgreSQL parts remained unaffected. However, we can actually reduce some of these conditionals to optimize the code.

close #28455
close #26422

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 @longbingljw, 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 focuses on refactoring database migration scripts to eliminate conditional logic based on the database dialect (PostgreSQL vs. MySQL). By standardizing column type definitions and removing database-specific checks, the changes aim to make the migration files cleaner, more concise, and easier to manage, particularly when adapting to different database systems like MySQL.

Highlights

• Migration Version Optimization: Simplified database migration scripts by removing redundant conditional logic that previously differentiated between PostgreSQL and MySQL. This streamlines the code and improves maintainability.
• Standardized Column Types: Replaced database-specific column type definitions (e.g., sa.Text() for PostgreSQL, models.types.LongText() for MySQL) with a unified, database-agnostic approach using models.types.LongText() or models.types.StringUUID() where appropriate.
• Code Cleanup: Removed the _is_pg helper function and associated conn = op.get_bind() calls from numerous migration files, further cleaning up the codebase.

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[gemini-code-assist]

Code Review

This pull request is a great refactoring effort to simplify the database migration files. By removing dialect-specific conditional logic (for PostgreSQL vs. MySQL) and using custom SQLAlchemy types (models.types.LongText, models.types.StringUUID, etc.), the migration scripts have become much cleaner, more readable, and easier to maintain. The changes are consistent across all modified files and correctly apply the intended abstraction. This significantly improves the codebase's portability and reduces redundancy. I've reviewed the changes and they look solid. Well done!

[longbingljw]

I will create a new pr to add seekdb logic in vector store and adapt for mysql