Bugfix: Support container-level SAS/SAT tokens for Azure backend

Restic previously expected SAS/SAT tokens to be generated at the account level,
which prevented tokens created at the container level from being used to
initialize a repository. This caused an error when attempting to initialize a
repository with container-level tokens.

Restic now supports both account-level and container-level SAS/SAT tokens for
initializing a repository.

https://github.com/restic/restic/issues/4004
https://github.com/restic/restic/pull/5093
