Add an event to allow alter the $payload before sending it to the client
>>> [!note] Migrated issue
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<!-- Migrated from issue #3557166. -->
Reported by: [giuseppe87](https://www.drupal.org/user/3521392)
Related to !1010
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p><code>/src/Base/OpenAiBasedProviderClientBase.php</code></p>
<p>Generates the $payload send to the provider in an hardcoded way.<br>
However, some service, like LiteLLM needs some metadata for some end-point, like <a href="https://docs.litellm.ai/docs/proxy/customers">Customers / End-User Budgets</a>.</p>
<p>It's necessary therefore to add extra information in those cases.</p>
<h3 id="summary-proposed-resolution">Proposed resolution</h3>
<p>Add an event subscriber to let other modules to alter the $payload.</p>
issue