Add CTAs to daily emails

Add a daily email CTA node type and reference field to attach a CTA to a
daily email.

Also update the RSS feed view to include the referenced body field
value.

modules/opd_daily_emails/src/Ctas.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\opd_daily_emails;
+
+use Drupal\node\NodeInterface;
+use Webmozart\Assert\Assert;
+
+final class Ctas {
+
+  public function isEmpty(): bool {
+    return empty($this->ctas);
+  }
+
+  public function getRandomCta(): NodeInterface {
+    return $this->ctas[array_rand($this->ctas)];
+  }
+
+  /**
+   * @param list<NodeInterface> $nodes
+   */
+  public static function fromNodes(array $nodes): self {
+    return new self($nodes);
+  }
+
+  /**
+   * @param list<NodeInterface> $ctas
+   */
+  private function __construct(
+    private array $ctas,
+  ) {
+    Assert::allIsInstanceOf($ctas, NodeInterface::class);
+  }
+
+}

modules/opd_daily_emails/src/DailyEmail.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\opd_daily_emails;
+
+use Drupal\node\Entity\Node;
+use Drupal\node\NodeInterface;
+
+final class DailyEmail extends Node implements NodeInterface {
+
+  public const NODE_TYPE = 'daily_email';
+
+}