CI: move grafana-build into pkg/build (#105640)

* move grafana-build into pkg/build

pkg/build/daggerbuild/fpm/builder.go

@@ -0,0 +1,14 @@
+package fpm
+
+import "dagger.io/dagger"
+
+const RubyContainer = "ruby:3.2.2-bullseye"
+
+func Builder(d *dagger.Client) *dagger.Container {
+	return d.Container().
+		From(RubyContainer).
+		WithEntrypoint(nil).
+		WithExec([]string{"gem", "install", "fpm"}).
+		WithExec([]string{"apt-get", "update"}).
+		WithExec([]string{"apt-get", "install", "-yq", "rpm", "gnupg2"})
+}