fix: update notice for users for clear-orphaned-file-records and remove-orphaned-files-on-storage commands

[kurokobo]

Summary

This is follow-up for #18835 to improve notice for users.

• The backup to be obtained before proceeding remove-orphaned-files-on-storage command should be from storage, not the database. I have corrected the wording.
• Since it may cause high load, I have made it display that running within the maintenance window is recommended.

Screenshots

Before	After

Before	After

Checklist

Important

Please review the checklist below before submitting your pull request.

• 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