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/toml/source-empty.go

@@ -0,0 +1,35 @@
+/**
+# Copyright 2024 NVIDIA CORPORATION
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package toml
+
+import (
+	"github.com/pelletier/go-toml"
+)
+
+type empty string
+
+var _ Loader = (*empty)(nil)
+
+// Load is a no-op for an empty source.
+func (e empty) Load() (*Tree, error) {
+	return newEmpty(), nil
+}
+
+func newEmpty() *Tree {
+	tomlTree, _ := toml.TreeFromMap(nil)
+	return (*Tree)(tomlTree)
+}