Fix: Doesn't automatically switch to alternative disks if the primary fails during configuration

[imhayatunnabi]

Laravel Backup package fails completely when any configured backup destination becomes unavailable due to network issues, storage problems, authentication failures, or service outages.

Current Problem:

• If any primary backup disk fails, the entire backup process fails
• No automatic retry mechanism for alternative storage destinations
• Users must manually intervene to switch to alternative backup locations
• Critical backups may be lost during infrastructure issues

Caused Problem Scenarios:

• AWS S3 outage
• Network connectivity
• Storage quota exceeded
• Authentication issues
• Service maintenance

Need to be this correct scenarios:

• Success Case: User gets BackupWasSuccessfulNotification (whether primary or fallback disk succeeded)
• Failure Case: User gets BackupHasFailedNotification (only if ALL disks including fallbacks failed)