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

* move grafana-build into pkg/build

pkg/build/daggerbuild/git/container_test.go

@@ -0,0 +1,17 @@
+package git
+
+import (
+	"testing"
+)
+
+func TestInjectURLCredentials(t *testing.T) {
+	expected := "https://username:password@example.org/somepath?query=param"
+	input := "https://example.org/somepath?query=param"
+	output, err := injectURLCredentials(input, "username", "password")
+	if err != nil {
+		t.Fatal("Unexpected error from injectURLCredentials:", err)
+	}
+	if expected != output {
+		t.Fatalf("Unexpected output. Expected '%s', got '%s'", expected, output)
+	}
+}