Add a way to extend the CLI with external binaries

This lets luet to be extended like git does (just by having luet-subcommand binaries under $PATH)
following the UNIX filosophy. It has the downside that we silence the errors from cobra and we handle
them by ourselves.

Also the Exec syscall is not portable, and it should have implementation for each platform (hence why in helpers)

cmd/root.go

@@ -16,6 +16,7 @@
 package cmd
 
 import (
+	"fmt"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -24,6 +25,7 @@ import (
 
 	"github.com/marcsauter/single"
 	config "github.com/mudler/luet/pkg/config"
+	helpers "github.com/mudler/luet/pkg/helpers"
 	. "github.com/mudler/luet/pkg/logger"
 	repo "github.com/mudler/luet/pkg/repository"
 
@@ -51,12 +53,13 @@ var RootCmd = &cobra.Command{
 			Fatal("failed to load configuration:", err.Error())
 		}
 	},
+	SilenceErrors: true,
 }
 
 func LoadConfig(c *config.LuetConfig) error {
 	// If a config file is found, read it in.
 	if err := c.Viper.ReadInConfig(); err != nil {
-		Warning(err)
+		Debug(err)
 	}
 
 	err := c.Viper.Unmarshal(&config.LuetCfg)
@@ -99,8 +102,18 @@ func Execute() {
 		}
 		defer s.TryUnlock()
 	}
+
 	if err := RootCmd.Execute(); err != nil {
-		Error(err)
+		if len(os.Args) > 0 {
+			for _, c := range RootCmd.Commands() {
+				if c.Name() == os.Args[1] {
+					os.Exit(-1) // Something failed
+				}
+			}
+			// Try to load a bin from path.
+			helpers.Exec("luet-"+os.Args[1], os.Args[1:], os.Environ())
+		}
+		fmt.Println(err)
 		os.Exit(-1)
 	}
 }