Prevent users from adding a leading slash to S3 destination folders

[crypdick]

Environment info

• Duplicati version: 2.0.7.1_beta_2023-05-25
• Operating system: Ubuntu 23.10
• Backend: S3 (wasabi)

Description

Using a leading slash in S3 destination folders causes Duplicati backups to fail after a few months. I think it would be sensible to disallow leading slashes in this setting. I detail my work-around here: https://forum.duplicati.com/t/found-remote-files-that-are-not-recorded-in-local-storage-please-run-repair-using-nas-as-destination/15830/19?u=crypdick

Steps to reproduce

1. Create S3 backup with a leading slash in the destination folder
2. Duplicati works for a few months without problems
3. One day backups stop working and you get a Found _ remote files that are not recorded in local storage, please run repair error. Hitting repair does not fix anything.

• Expected result:
  I think Duplicati should prevent you from creating objects keys with a leading double-slash, which is almost certainly an accident.