Move hook to event

Hi I started to add event, but is missing to dispatch it.

This is a great start. The missing piece here is that we don't create or own this event, it belongs to search_api_solr.

See https://www.drupal.org/project/search_api_solr/issues/3203375 ✨ Introduce events and deprecate hooks Fixed

We need an EventSusbscriber service that response to \Drupal\search_api_solr\Event\PostCreateIndexDocumentsEvent

I have made an attempt to move the code from search_api_federated_solr_search_api_solr_documents_alter into an event subscriber.

Importantly, I had to use:
$documents = $event->getSolariumDocuments();

To get the list of documents, and at the end of the function I call:
$event->setSolariumDocuments($documents);

I was following the annotation in search_api_solr's Event class:

<?php

namespace Drupal\search_api_solr\Event;

/**
 * Event to be fired after all solarium documents
 * have been created for indexing.
 *
 * @code
 *   // Add a "foo" field with value "bar" to all documents.
 *   $documents = $event->getSolariumDocuments();
 *   foreach ($documents as $document) {
 *     $document->setField('foo', 'bar');
 *   }
 *   $event->setSolariumDocuments($documents):
 * @endcode
 *
 * @Event
 */
final class PostCreateIndexDocumentsEvent extends AbstractSearchApiItemsSolariumDocumentsEvent {}

Hi @ddavisboxleitner I reviewed it.

No bugs found
Changes applied correctly.

I'm using drupal 10.1 version and branch 4.x

Module is ok.

Moving to RTBC.