CI: add the grabpl build-backend command into the repo (#52673)

* Move the grabpl build-backend command and clean it up a bit

pkg/build/executil/exec.go

@@ -0,0 +1,46 @@
+package executil
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+func RunAt(ctx context.Context, dir, cmd string, args ...string) error {
+	// Ignore gosec G204 as this function is only used in the build process.
+	//nolint:gosec
+	c := exec.CommandContext(ctx, cmd, args...)
+	c.Dir = dir
+
+	b, err := c.CombinedOutput()
+
+	if err != nil {
+		return fmt.Errorf("%w. '%s %v': %s", err, cmd, args, string(b))
+	}
+
+	return nil
+}
+
+func Run(ctx context.Context, cmd string, args ...string) error {
+	return RunAt(ctx, ".", cmd, args...)
+}
+
+func OutputAt(ctx context.Context, dir, cmd string, args ...string) (string, error) {
+	// Ignore gosec G204 as this function is only used in the build process.
+	//nolint:gosec
+	c := exec.CommandContext(ctx, cmd, args...)
+	c.Dir = dir
+
+	b, err := c.CombinedOutput()
+
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(string(b)), nil
+}
+
+func Output(ctx context.Context, cmd string, args ...string) (string, error) {
+	return OutputAt(ctx, ".", cmd, args...)
+}