feat(customers): tambahkan request validasi untuk pelanggan

- Menambahkan kelas CustomerRequest untuk menangani validasi data pelanggan.
- Aturan validasi mencakup:
  - customer_code: wajib, string, maksimal 20 karakter, unik di tabel customers.
  - name: wajib, string, maksimal 100 karakter.
  - address: wajib, string.
  - branch_code: wajib, string, maksimal 3 karakter, harus ada di tabel branches.
  - date_of_birth: opsional, tanggal.
  - email: opsional, string, maksimal 100 karakter, format email.
- Memperbarui aturan untuk customer_code saat metode PUT.

app/Http/Requests/CustomerRequest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Modules\Webstatement\Http\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class CustomerRequest extends FormRequest
+{
+    /**
+     * Get the validation rules that apply to the request.
+     */
+    public function rules()
+    : array
+    {
+        $rules = [
+            'customer_code' => 'required|string|max:20|unique:customers,customer_code',
+            'name' => 'required|string|max:100',
+            'address' => 'required|string',
+            'branch_code' => 'required|string|max:3|exists:branches,code',
+            'date_of_birth' => 'nullable|date',
+            'email' => 'nullable|string|max:100|email',
+        ];
+
+        if ($this->method() == 'PUT') {
+            $rules['customer_code'] = 'required|string|max:20|unique:customers,customer_code,' . $this->id;
+        }
+
+        return $rules;
+    }
+
+    public function authorize()
+    : bool
+    {
+        return true;
+    }
+}