errors: standardize error wrapping for Fatal errors

* replace all occurences of  `errors.Fatal(err.Error())` with `errors.Fatalf("%s", err)` so that the error wrapping is correct across the codebase

* updated the review comments

cmd/restic/cmd_init.go

@@ -101,7 +101,7 @@ func runInit(ctx context.Context, opts InitOptions, gopts GlobalOptions, args []
 		PackSize:    gopts.PackSize * 1024 * 1024,
 	})
 	if err != nil {
-		return errors.Fatal(err.Error())
+		return errors.Fatalf("%s", err)
 	}
 
 	err = s.Init(ctx, version, gopts.password, chunkerPolynomial)