feat: add config:clear command

Closes #3537

plugins/config/src/subcommands/clear/clear.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"flag"
+	"os"
+
+	"github.com/dokku/dokku/plugins/config"
+)
+
+//clear all entries from the given environment
+func main() {
+	args := flag.NewFlagSet("config:clear", flag.ExitOnError)
+	global := args.Bool("global", false, "--global: use the global environment")
+	noRestart := args.Bool("no-restart", false, "--no-restart: no restart")
+	args.Parse(os.Args[2:])
+	config.CommandClear(args.Args(), *global, *noRestart)
+}