feat: implement builder plugin

This plugin will allow users to override the builder used for their application, enabling users to use custom builders if desired.

plugins/builder/src/triggers/triggers.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/dokku/dokku/plugins/builder"
+	"github.com/dokku/dokku/plugins/common"
+)
+
+// main entrypoint to all triggers
+func main() {
+	parts := strings.Split(os.Args[0], "/")
+	trigger := parts[len(parts)-1]
+	flag.Parse()
+
+	var err error
+	switch trigger {
+	case "builder-detect":
+		appName := flag.Arg(0)
+		err = builder.TriggerBuilderDetect(appName)
+	case "install":
+		err = builder.TriggerInstall()
+	case "post-delete":
+		appName := flag.Arg(0)
+		err = builder.TriggerPostDelete(appName)
+	case "report":
+		appName := flag.Arg(0)
+		err = builder.ReportSingleApp(appName, "", "")
+	default:
+		err = fmt.Errorf("Invalid plugin trigger call: %s", trigger)
+	}
+
+	if err != nil {
+		common.LogFailWithError(err)
+	}
+}