Implement plugin catalog and discovery system

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

internal/plugin/exec_unix.go

@@ -0,0 +1,30 @@
+//go:build !windows
+
+/*
+Copyright 2026 The Flux authors
+
+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 plugin
+
+import (
+	"os"
+	"syscall"
+)
+
+// Exec replaces the current process with the plugin binary.
+// This is what kubectl does — no signal forwarding or exit code propagation needed.
+func Exec(path string, args []string) error {
+	return syscall.Exec(path, append([]string{path}, args...), os.Environ())
+}