refactor: move all port management code to standalone ports plugin

This change makes interacting with port mappings more clear - folks might previously set the port mapping to the proxy type or vice-versa.

The existing proxy:ports* commands still exist but will show a deprecation warning for a single minor release.

plugins/ports/src/commands/commands.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/dokku/dokku/plugins/common"
+)
+
+const (
+	helpHeader = `Usage: dokku ports[:COMMAND]
+
+Manage ports for an app
+
+Additional commands:`
+
+	helpContent = `
+    ports:list <app>, List port mappings for app
+    ports:add <app> [<scheme>:<host-port>:<container-port>...], Add port mappings to an app
+    ports:clear <app>, Clear all port mappings for an app
+    ports:remove <app> [<host-port>|<scheme>:<host-port>:<container-port>...], Remove specific port mappings from an app
+    ports:set <app> [<scheme>:<host-port>:<container-port>...], Set port mappings for an app
+    ports:report [<app>] [<flag>], Displays a ports report for one or more apps
+`
+)
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+
+	cmd := flag.Arg(0)
+	switch cmd {
+	case "ports", "ports:help":
+		usage()
+	case "help":
+		command := common.NewShellCmd(fmt.Sprintf("ps -o command= %d", os.Getppid()))
+		command.ShowOutput = false
+		output, err := command.Output()
+
+		if err == nil && strings.Contains(string(output), "--all") {
+			fmt.Println(helpContent)
+		} else {
+			fmt.Print("\n    ports, Manage ports for an app\n")
+		}
+	default:
+		dokkuNotImplementExitCode, err := strconv.Atoi(os.Getenv("DOKKU_NOT_IMPLEMENTED_EXIT"))
+		if err != nil {
+			fmt.Println("failed to retrieve DOKKU_NOT_IMPLEMENTED_EXIT environment variable")
+			dokkuNotImplementExitCode = 10
+		}
+		os.Exit(dokkuNotImplementExitCode)
+	}
+}
+
+func usage() {
+	common.CommandUsage(helpHeader, helpContent)
+}