Refactor Toml config handling

This change refactors the toml config file handlig for runtimes
such as containerd or crio. A toml.Loader is introduced that
encapsulates loading the required file.

This can be extended to allow other mechanisms for loading
loading the current config.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

pkg/config/engine/docker/docker.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/logger"
+	"github.com/NVIDIA/nvidia-container-toolkit/pkg/config"
 	"github.com/NVIDIA/nvidia-container-toolkit/pkg/config/engine"
 )
 
@@ -128,6 +129,6 @@ func (c Config) Save(path string) (int64, error) {
 		return 0, fmt.Errorf("unable to convert to JSON: %v", err)
 	}
 
-	n, err := engine.Config(path).Write(output)
+	n, err := config.Raw(path).Write(output)
 	return int64(n), err
 }