Add required option to new toml config

This change adds a "required" option to the new toml config
that controls whether a default config is returned or not.
This is useful from the NVIDIA Container Runtime Hook, where
/run/driver/nvidia/etc/nvidia-container-runtime/config.toml
is checked before the standard path.

This fixes a bug where the default config was always applied
when this config was not used.

See https://github.com/NVIDIA/nvidia-container-toolkit/issues/106

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

cmd/nvidia-container-runtime-hook/hook_config.go

@@ -45,6 +45,7 @@ func loadConfig() (*config.Config, error) {
 	for _, p := range configPaths {
 		cfg, err := config.New(
 			config.WithConfigFile(p),
+			config.WithRequired(true),
 		)
 		if err == nil {
 			return cfg.Config()