Validate write permissions on backup destination

[DavidePrincipi]

When a new backup destination is added and its settings are validated, try to create a remote file to ensure write permissions are granted.

Refs https://community.nethserver.org/t/ns8-backup-failing-on-idrive-e2-s3/24936/3

Thanks to Dan

[DavidePrincipi]

UI changes:

• Remove the Open Notification Drawer button, because it silently closes the modal window. Field values are lost and they must be typed again.
• Catch the new backend error codes and show the corresponding notification, as detailed in the table below.

error code	title	description
no_read_permission	Read access error	Cannot connect, authenticate, or read from the backup destination.
no_write_permission	Write access error	Cannot create files or directories on the backup destination. Check write permissions.
no_delete_permission	Delete access error	Cannot delete files or directories from the backup destination. Check delete permissions.
backup_repository_not_accessible	Configuration error	Cannot access the backup destination. Check the error notification or System logs for details.

Discussion about UI error handling: https://mattermost.nethesis.it/nethesis/pl/8g6smkqoiibcfg1qxyh4338g4e