* Use Credential from BSL for restic commands

This change introduces support for restic to make use of per-BSL
credentials. It makes use of the `credentials.FileStore` introduced in
PR #3442 to write the BSL credentials to disk. To support per-BSL
credentials for restic, the environment for the restic commands needs to
be modified for each provider to ensure that the credentials are
provided via the correct provider specific environment variables.
This change introduces a new function `restic.CmdEnv` to check the BSL
provider and create the correct mapping of environment variables for
each provider.

Previously, AWS and GCP could rely on the environment variables in the
Velero deployments to obtain the credentials file, but now these
environment variables need to be set with the path to the serialized
credentials file if a credential is set on the BSL.

For Azure, the credentials file in the environment was loaded and parsed
to set th...