enh: rsma docs and task monitor

[kailixu]

Description

Please briefly describe the code changes in this pull request.

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @kailixu, 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 RSMA (Rollup Small Materialized Aggregation) feature by updating its Chinese documentation with new usage examples and introducing commands to monitor and terminate RSMA tasks. Concurrently, it refactors the underlying system logic to incorporate database UIDs in task management, improving the accuracy and robustness of operations like compacting, scanning, and retention, particularly when checking for database existence. These changes aim to provide clearer user guidance and more reliable internal task handling.

Highlights

• RSMA Documentation Enhancement: The Chinese documentation for Rollup SMA (RSMA) has been updated to include new commands for monitoring and managing RSMA tasks, along with corrected syntax and usage examples.
• Task Monitoring and Management: New capabilities have been added to display and terminate RSMA tasks using show retentions, show retention {id}, and kill retention {id} commands, improving operational control.
• Database UID Integration: Internal system logic has been refactored to incorporate database UIDs (Unique Identifiers) into compact, scan, and retention task objects, enhancing the robustness and accuracy of database existence checks and task management.
• Error Code Refactoring: An internal error code, TSDB_CODE_MND_INVALID_TRIM_ID, has been renamed to TSDB_CODE_MND_INVALID_RETENTION_ID for better clarity and consistency with the retention task terminology.

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[gemini-code-assist]

Code Review

This pull request introduces documentation and monitoring capabilities for RSMA (Rollup Small Materialized Aggregation), including commands to show and kill RSMA tasks. A significant part of the changes involves a refactoring to use a database UID (dbUid) for more robust database existence checks in background tasks like compaction, scan, and retention. This is a good improvement for correctness. The error codes and function names related to retention tasks have also been clarified for better consistency.

My review has identified a critical null pointer dereference bug in mndDbIsExist that could lead to a crash. I've also provided a suggestion to improve the clarity of an example in the RSMA documentation.