feat: correctly delete applications using Celery workers

[chazzhou]

Description

This PR implements a robust application deletion process using Celery workers. The change ensures that app deletion is handled asynchronously, improving system reliability and laying the groundwork for better user experience. It includes the deletion of all related data, including tag bindings.

However, more work is needed to implement polling or WebSocket for actual front-end status updates. This PR focuses on the backend implementation and prepares the system for future frontend enhancements.

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Manually triggered app deletion and verified in the database that all related data (including tag bindings) are properly deleted
• Tested error scenarios by intentionally causing failures in the deletion process
• Verified that the Celery task retry mechanism works as expected

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods
• optional I have made corresponding changes to the documentation
• optional I have added tests that prove my fix is effective or that my feature works
• optional New and existing unit tests pass locally with my changes

[chazzhou]

cc. @crazywoola

[laipz8200]

Thank you for your PR! Could you please open an issue first, providing a detailed description of the problem, and include the issue link in this PR? This will help us quickly understand and review your PR.

[laipz8200]

I still have a few questions. Please check the comments I left in the code.

[laipz8200]

Great! Thank you.