Add option to disable Linkchecker (esp. entity hooks)

Problem/Motivation

We're using lovely Linkchecker in a large project and just had to run a batch update on many entities. We were wondering why it became extremely slow and saw MANY Linkchecker queries causing this.

I tried #3313343: Add option to disable cron activity, but then had to find out that it's not a cron thing, but Linkchecker also uses hook_entity_* a lot:

/**
 * Implements hook_cron().
 */
function linkchecker_cron() {
  if (\Drupal::config('linkchecker.settings')->get('check.disable_cron')) {
    return;
  }
  \Drupal::service('linkchecker.extractor_batch')->processEntities();
  \Drupal::service('linkchecker.checker')->queueLinks();
}

/**
 * Implements hook_entity_insert().
 */
function linkchecker_entity_insert(EntityInterface $entity) {
  if ($entity instanceof LinkCheckerLinkInterface) {
    return;
  }

  if ($entity instanceof FieldableEntityInterface && !$entity->isNew()) {
    /** @var \Drupal\linkchecker\LinkExtractorService $extractor */
    $extractor = \Drupal::service('linkchecker.extractor');
    $links = $extractor->extractFromEntity($entity);

    if (!empty($links)) {
      $extractor->saveLinkMultiple($links);
      $extractor->updateEntityExtractIndex($entity);
    }

    \Drupal::service('linkchecker.clean_up')->cleanUpForEntity($entity);
  }
}

/**
 * Implements hook_entity_update().
 */
function linkchecker_entity_update(EntityInterface $entity) {
  if ($entity instanceof LinkCheckerLinkInterface) {
    return;
  }

  if ($entity instanceof FieldableEntityInterface) {
    /** @var \Drupal\linkchecker\LinkExtractorService $extractor */
    $extractor = \Drupal::service('linkchecker.extractor');
    $links = $extractor->extractFromEntity($entity);

    if (!empty($links)) {
      $extractor->saveLinkMultiple($links);
      $extractor->updateEntityExtractIndex($entity);
    }

    \Drupal::service('linkchecker.clean_up')->cleanUpForEntity($entity);
  }
}

/**
 * Implements hook_entity_delete().
 */
function linkchecker_entity_delete(EntityInterface $entity) {
  if ($entity instanceof LinkCheckerLinkInterface) {
    \Drupal::service('linkchecker.clean_up')->cleanUpQueues($entity->id());
    return;
  }

  if ($entity instanceof FieldableEntityInterface) {
    \Drupal::service('linkchecker.clean_up')->cleanUpForEntity($entity);
  }
}

As Drupal 8+ has no "disable module" functionality, there's no way to disable it. Uninstalling removes configuration and all LinkChecker entities.

So it would be great to have a simple setting to disable linkchecker (for a while)!

Disabling link checker on cron run should still be a separate setting (#3313343: Add option to disable cron activity) as the use-cases for both are different.

Workaround

As a workaround I just commented out these hooks now, but that's not a nice user-facing solution. After doing that, the batch ran fast again!

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes