Add drop-in file support for containerd and crio

This change adds drop-in file support for containerd and crio.
Instead of writing the entire in-memory config to the specified
config path, we write only the modified settings (nvidia runtimes,
default runtime, enable_cdi) settings to a drop-in file and update
the top-level configs to import this if required.

Signed-off-by: Evan Lezar <elezar@nvidia.com>
Co-authored-by: Carlos Eduardo Arango Gutierrez <eduardoa@nvidia.com>

Author: elezar

cmd/nvidia-ctk-installer/container/container.go

@@ -35,6 +35,8 @@ const (
 
 // Options defines the shared options for the CLIs to configure containers runtimes.
 type Options struct {
+	DropInConfig string
+	// TODO: Rename to TopLevelConfig
 	Config string
 	Socket string
 	// ExecutablePath specifies the path to the container runtime executable.
@@ -71,8 +73,12 @@ func (o Options) Unconfigure(cfg engine.Interface) error {
 
 // flush flushes the specified config to disk
 func (o Options) flush(cfg engine.Interface) error {
-	logrus.Infof("Flushing config to %v", o.Config)
-	n, err := cfg.Save(o.Config)
+	filepath := o.DropInConfig
+	if filepath == "" {
+		filepath = o.Config
+	}
+	logrus.Infof("Flushing config to %v", filepath)
+	n, err := cfg.Save(filepath)
 	if err != nil {
 		return fmt.Errorf("unable to flush config: %v", err)
 	}