fetch current container runtime config through the command line

Signed-off-by: Tariq Ibrahim <tibrahim@nvidia.com>

add default runtime binary path to runtimes field of toolkit config toml

Signed-off-by: Tariq Ibrahim <tibrahim@nvidia.com>

[no-relnote] Get low-level runtimes consistently

We ensure that we use the same low-level runtimes regardless
of the runtime engine being configured. This ensures consistent
behaviour.

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

Co-authored-by: Evan Lezar <elezar@nvidia.com>

address review comment

Signed-off-by: Tariq Ibrahim <tibrahim@nvidia.com>

pkg/config/engine/engine.go

@@ -0,0 +1,63 @@
+/**
+# 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 engine
+
+import "strings"
+
+// GetBinaryPathsForRuntimes returns the list of binary paths for common runtimes.
+// The following list of runtimes is considered:
+//
+//	the default runtime, "runc", and "crun"
+//
+// If an nvidia* runtime is set as the default runtime, this is ignored.
+func GetBinaryPathsForRuntimes(cfg Interface) []string {
+
+	var binaryPaths []string
+	seen := make(map[string]bool)
+	for _, runtime := range GetLowLevelRuntimes(cfg) {
+		runtimeConfig, err := cfg.GetRuntimeConfig(runtime)
+		if err != nil {
+			// TODO: It will be useful to log the error when GetRuntimeConfig fails for a runtime
+			continue
+		}
+		binaryPath := runtimeConfig.GetBinaryPath()
+		if binaryPath == "" || seen[binaryPath] {
+			continue
+		}
+		seen[binaryPath] = true
+		binaryPaths = append(binaryPaths, binaryPath)
+	}
+
+	return binaryPaths
+}
+
+// GetLowLevelRuntimes returns a predefined list low-level runtimes from the specified config.
+// nvidia* runtimes are ignored.
+func GetLowLevelRuntimes(cfg Interface) []string {
+	var runtimes []string
+	isValidDefault := func(s string) bool {
+		if s == "" {
+			return false
+		}
+		// ignore nvidia* runtimes.
+		return !strings.HasPrefix(s, "nvidia")
+	}
+	if defaultRuntime := cfg.DefaultRuntime(); isValidDefault(defaultRuntime) {
+		runtimes = append(runtimes, defaultRuntime)
+	}
+	return append(runtimes, "runc", "crun")
+}