Add backup-taget connection status

Ref: https://github.com/harvester/harvester/issues/2631

Verified this feature has been implemented.

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Test Information

  • Environment: qemu/KVM 2 nodes
  • Harvester Version: master-032742f0-head
  • ui-source Option: Auto

Verify Steps:

  1. Install Harvester with any nodes
  2. Login to Dashboard then navigate to Advanced/Settings
  3. Setup a invalid NFS/S3 backup-target, then click Test connection button, error message should displayed
  4. Setup a valid NFS/S3 backup-target, then click Test connection button, notify message should displayed
  5. Navigate to Advanced/VM Backups, notify message should NOT displayed
  6. Navigate to Advanced/Settings and stop the backup-target server, then navigate to Advanced/VM Backups, error message should displayed