[FEATURE] Allow disabling resources

Pretty straight forward thanks to the plugin system!

EDIT The following code has been deprecated, use the variant in the next comment instead to disable resources.

/**
 * Alter the resource definitions.
 *
 * @param array $plugins
 *   An array of plugin definitions.
 */
function jsonapi_jsonapi_resource_info_alter(&$plugins) {
  foreach (array_keys($plugins) as $plugin_id) {
    // Set the 'enabled' property to false if the plugin definition is not for a
    // node.
    $plugins[$plugin_id]['enabled'] = $plugins[$plugin_id]['entityType'] === 'node';
  }
}

The previous code has been deprecated in favor of:

/**
 * Alter the resource definitions.
 *
 * @param \Drupal\jsonapi\Configuration\ResourceConfigInterface[] $resources
 *   An array of plugin definitions.
 */
function jsonapi_jsonapi_resources_alter(&$resources) {
  foreach ($resources as &$resource) {
    // Set the 'enabled' property to false if the plugin definition is for a
    // node_type.
    if (in_array($resource->getEntityTypeId(), ['node_type', 'taxonomy_term'])) {
      $resource->disable();
    }
  }
}

This was introduced in #2807185: [BUGFIX] Handle relationships when target resource is not accessible.