Add validation rule for subscription steps

app/Rules/Subscriptions/Steps.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace App\Rules\Subscriptions;
+
+use App\Services\Subscription\StepService;
+use Closure;
+use App\Livewire\BillingPortal\Purchase;
+use Illuminate\Contracts\Validation\ValidationRule;
+
+class Steps implements ValidationRule
+{
+    /**
+     * Run the validation rule.
+     *
+     * @param  \Closure(string): \Illuminate\Translation\PotentiallyTranslatedString  $fail
+     */
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        $steps = StepService::mapToClassNames($value);
+        $errors = StepService::check($steps);
+
+        if (count($errors) > 0) {
+            $fail($errors[0]);
+        }
+    }
+}