CI: move grabpl build-frontend from grabpl to grafana (#53073)

* move grabpl build-frontend

pkg/build/cmd/buildfrontend.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"log"
+	"strings"
+
+	"github.com/grafana/grafana/pkg/build/errutil"
+	"github.com/grafana/grafana/pkg/build/frontend"
+	"github.com/grafana/grafana/pkg/build/syncutil"
+	"github.com/urfave/cli/v2"
+)
+
+func BuildFrontend(c *cli.Context) error {
+	version := ""
+	if c.NArg() == 1 {
+		version = strings.TrimPrefix(c.Args().Get(0), "v")
+	}
+
+	cfg, mode, err := frontend.GetConfig(c, version)
+	if err != nil {
+		return err
+	}
+
+	p := syncutil.NewWorkerPool(cfg.NumWorkers)
+	defer p.Close()
+
+	g, _ := errutil.GroupWithContext(c.Context)
+	if err := frontend.Build(mode, frontend.GrafanaDir, p, g); err != nil {
+		return err
+	}
+	if err := g.Wait(); err != nil {
+		return err
+	}
+
+	log.Println("Successfully built Grafana front-end!")
+
+	return nil
+}