repository: Push all usage of errors.Fatal out of the package

As the `Fatal` error type only includes a string, it becomes impossible
to inspect the contained error. This is for a example a problem for the
fuse implementation, which must be able to detect context.Canceled
errors.

Co-authored-by: greatroar <61184462+greatroar@users.noreply.github.com>

cmd/restic/global.go

@@ -456,7 +456,7 @@ func OpenRepository(ctx context.Context, opts GlobalOptions) (*repository.Reposi
 		PackSize:    opts.PackSize * 1024 * 1024,
 	})
 	if err != nil {
-		return nil, err
+		return nil, errors.Fatal(err.Error())
 	}
 
 	passwordTriesLeft := 1