Enhancement: Allow usage of deprecated S3 ListObjectsV1 API

Restic didn't work with some S3 API implementations that don't have a
working ListObjectsV2 API endpoint. This concerns mainly Ceph versions
before v14.2.5 , but may impact other S3 API implementations.

Restic now allows selection of the older ListObjectsV1 endpoint by using
the 's3.list-objects-v1' extended option, for instance:

`restic -o s3.list-objects-v1=true snapshots`

https://github.com/restic/restic/issues/3083
https://github.com/restic/restic/pull/3085