Provide the query count

This is related to #2746939: [FEATURE] Add pagination metadata.

The query count totally can be helpful, but I suggest to not expose it by default. Counting all elements can be a huge performance loss.

Like @dawehner suggested, we should make sure this behavior is opt-in.

I see this as a global configuration. You either add counts everywhere or nowhere.

It doesn't account for the configuration options being discussed here, but for anyone using already using the work in #2746939: [FEATURE] Add pagination metadata as well, I've shared an updated patch to include the total result count in the meta section as described here.

See #2746939-49: [FEATURE] Add pagination metadata for the patch and interdiff specifically adding this to the meta section.

This patch adds an include_count config value to the schema and adds a form element on the settings form for setting it. Configurable resource types then look at this global value when deciding the result of their includeCount method.

For more background, see https://www.drupal.org/node/2746939#comment-12136652

I made two minor changes on commit.

1. +++ b/src/ResourceType/ConfigurableResourceType.php
   @@ -27,6 +28,11 @@ class ConfigurableResourceType extends ResourceType {
   +   * @var ConfigFactoryInterface
   

   We need the FQN.

2. +++ b/src/ResourceType/ConfigurableResourceType.php
   @@ -40,11 +46,12 @@ class ConfigurableResourceType extends ResourceType {
       * @param \Drupal\jsonapi_extras\Plugin\ResourceFieldEnhancerManager $enhancer_manager
       *   Plugin manager for enhancers.
       */
   -  public function __construct($entity_type_id, $bundle, $deserialization_target_class, JsonapiResourceConfig $resource_config, ResourceFieldEnhancerManager $enhancer_manager) {
   +  public function __construct($entity_type_id, $bundle, $deserialization_target_class, JsonapiResourceConfig $resource_config, ResourceFieldEnhancerManager $enhancer_manager, ConfigFactoryInterface $config_factory) {
   

   The docblock for the new parameter is missing.