refactor: decrease compile time for golang plugins

This change refactors the compiled golang plugins into 3 distinct binaries:

- commands: already existing
- subcommands/subcommands: entrypoint into all subcommands
- triggers: entrypoint into all triggers

It then further symlinks triggers and subcommands to the built binaries. This results in both a much faster build process as well as smaller package size.

plugins/repo/src/triggers/pre-delete/pre-delete.go

@@ -1,19 +0,0 @@
-package main
-
-import (
-	"flag"
-
-	"github.com/dokku/dokku/plugins/common"
-	"github.com/dokku/dokku/plugins/repo"
-)
-
-// destroys the buildpacks property for a given app container
-func main() {
-	flag.Parse()
-	appName := flag.Arg(0)
-
-	err := repo.PurgeCache(appName)
-	if err != nil {
-		common.LogFail(err.Error())
-	}
-}

plugins/repo/src/triggers/triggers.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/dokku/dokku/plugins/common"
+	"github.com/dokku/dokku/plugins/repo"
+)
+
+// 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 "pre-delete":
+		appName := flag.Arg(0)
+		err = repo.PurgeCache(appName)
+	default:
+		common.LogFail(fmt.Sprintf("Invalid plugin trigger call: %s", trigger))
+	}
+
+	if err != nil {
+		common.LogFail(err.Error())
+	}
+}