Enhancement: Certificates can be passed through environment variables
Restic will now read the paths to the certificates from the environment
variables `RESTIC_CACERT` or `RESTIC_TLS_CLIENT_CERT` if `--cacert` or
`--tls-client-cert` are not specified.
https://github.com/restic/restic/issues/1926
https://github.com/restic/restic/pull/4384