feat(01-purchase-data-layer): add post-payment purchase data layer

Phase 1 complete:

- move purchase event to order confirmation after successful payment

- add backend purchase payload builder for transaction and ticket lines

- remove premature purchase push from przelewy24 redirect view

templates/tickets/order-confirm.php

@@ -1,3 +1,21 @@
+<?php
+$purchaseDataLayerJson = null;
+if (is_array($this->purchase_data_layer ?? null)) {
+  $purchaseDataLayerJson = json_encode(
+    $this->purchase_data_layer,
+    JSON_HEX_TAG | JSON_HEX_AMP | JSON_HEX_APOS | JSON_HEX_QUOT | JSON_INVALID_UTF8_SUBSTITUTE
+  );
+}
+?>
+
+<?php if($purchaseDataLayerJson) : ?>
+<script type="text/javascript">
+window.dataLayer = window.dataLayer || [];
+window.dataLayer.push({ ecommerce: null });
+window.dataLayer.push(<?= $purchaseDataLayerJson; ?>);
+</script>
+<?php endif; ?>
+
 <?php if($this->order_successful === true) : ?>
 <script type="text/javascript">
 $.alert({
@@ -175,4 +193,4 @@ $.alert({
       </div>
     </div>
   </div>
-</div>
+</div>