Allow to alter collection names

In the current implementation the Search API index name is used when the Typesense collection is created. This has caused some confusion in the code base for interacting with the schema:

Using the index ID
Sometimes we are retrieving the schema using the index ID, example:

src/Controller/TypesenseIndexController.php
62:    $schema = $backend->getSchema($search_api_index->id())?->getSchema();

Using the collection name
Sometimes we are retrieving the schema using the collection name, example:

src/Plugin/search_api/backend/SearchApiTypesenseBackend.php
407:    $schema = $this->getSchema($collection);

Since in 100% of the cases, the collection name is derived from the index, let's standardize this on the index.

Many methods in TypesenseClientInterface are taking a collection name as an argument, for example:

  /**
   * Removes a Typesense index.
   *
   * @param string|null $collection_name
   *   The name of the index to remove.
   */
  public function dropCollection(?string $collection_name): void;

In the current code base, since the collection name was always equal to the index ID, we were often passing in the index ID in lieu of the collection name, here is an example from SearchApiTypesenseBackend::removeIndex()

$this->getTypesenseClient()->dropCollection($index->id());

We should change this everywhere to use the collection name instead, so we properly decouple the collections from indexes. It will become:

$collection_name = $this->getCollectionName($index);
$this->getTypesenseClient()->dropCollection($collection_name);

In order to facilitate this, we should make SearchApiTypesenseBackend::getCollectionName() public so we can easily get the collection name for a given index.

Next up, we can improve and simplify the ::getCollectionName() method. It currently works like this:

  public function getCollectionName(?IndexInterface $index): ?string {
    if ($index == NULL) {
      return NULL;
    }

    try {
      /** @var \Drupal\search_api_typesense\Entity\TypesenseSchemaInterface $typesense_schema */
      $typesense_schema = $this->entityTypeManager
        ->getStorage('typesense_schema')
        ->load($index->id());

      if ($typesense_schema == NULL) {
        return NULL;
      }

      return $typesense_schema->id();
    }
    catch (InvalidPluginDefinitionException | PluginNotFoundException $e) {
      return NULL;
    }
  }

So basically the logic is:

2. Get the index ID.
3. Load the TypesenseSchema entity with the same ID.
4. If it exists, return the ID of the entity we just loaded.

But since both the index and the schema entities have exactly the same ID, this whole logic can be reduced to:

  public function getCollectionName(?IndexInterface $index): ?string {
    return $index?->id();
  }

I also think it doesn't make any sense to allow passing in NULL for $index, and we should also not allow NULL to be returned. So this can become:

  public function getCollectionName(IndexInterface $index): string {
    return $index->id();
  }

When creating a collection, the name of the collection is part of the schema that is passed to the Typesense server, so we need to make sure the altered collection name is set on the schema.

And finally we can introduce an event that can be used to alter the collection name.

Thanks for the review! I will address the remarks,