Add validation to determineFieldConfigurations
>>> [!note] Migrated issue
<!-- Drupal.org comment -->
<!-- Migrated from issue #3507109. -->
Reported by: [marcus_johansson](https://www.drupal.org/user/385947)
Related to !57
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p>Error: Cannot use object of type Drupal\ai\OperationType\Chat\ChatMessage as array in Drupal\ai_agents\Plugin\AiAgent\FieldType->storeFieldConfigurations() (line 419 of /var/www/html/web/modules/contrib/ai_agents/src/Plugin/AiAgent/FieldType.php).</p>
<p>#0 /var/www/html/web/modules/contrib/ai_agents/src/Plugin/AiAgent/FieldType.php(663): Drupal\ai_agents\Plugin\AiAgent\FieldType->storeFieldConfigurations()<br>
#1 /var/www/html/web/modules/contrib/ai_agents/src/Plugin/AiAgent/FieldType.php(312): Drupal\ai_agents\Plugin\AiAgent\FieldType->createField()</p>
issue