The region value used for backups on S3-compatible services
is now saved correctly even if the user changes the configuration
from backup of type S3 to another.
Starting from the versions subsequent to the v57a, the default backend
of duplicity for backups to S3-compatible services is boto3
which requires the indication of the region (--S3-region-name)
for most cases in which the S3 service is not provided by AWS.
Thanks to this intervention, the region of the S3 service
is provided as a parameter to duplicity and is stored in the
/home/user-data/backup/custom.yaml file, like any other backup
configuration parameters.
Moreover, the list of the regions shown to the user in the drop-down
menu in the backup configuration panel is replaced with
a normal text field, since the list included the AWS regions only
and therefore was not usable in all other cases.
See issue #2200.