Support for Entity Construction Kit (ECK)

We merged the latest commits from ✨ Provide Drush command to enforce configs Fixed , which allowed us to avoid the looping behaviour with ECK.

We then added:

1. Tests and a test module to ensure that Config Enforce supports Entity Construction Kit (ECK).
2. Tests and a test module to ensure that Config Enforce supports nested references between ECK bundles.
3. Tests and a test module to ensure that Config Enforce supports nested references between ECK bundles in the same target module.

This appears to show that " 2. Dependencies not resolving properly" is not at issue.

That said, we are seeing the following output at the end of each of our tests:
```
│
╳ The "test_eck_entity_type" entity type does not exist. (Drupal\Core\Entity\EntityStorageException)
│
└─ @AfterScenario # CEI\CeiDrupalContext::cleanUsers()
│
╳ The "test_eck_entity_type" entity type does not exist. (Drupal\Core\Entity\EntityStorageException)
│
└─ @AfterScenario # Drupal\DrupalExtension\Context\MessageContext::cleanUsers()
│
╳ The "test_eck_entity_type" entity type does not exist. (Drupal\Core\Entity\EntityStorageException)
│
└─ @AfterScenario
```

Despite this, the tests themselves are all passing.

The plan, at this point, is to add Inline Entity Form (IEF) to the mix (with its simple form). If that doesn't trigger dependency errors, we'll try adding in Conditional forms, then apply some of the patched in-use on the client project.

Running with extra verbosity (behat -vv) got us:

  │
  ╳  Drupal\Core\Entity\EntityStorageException: The "test_eck_entity_type" entity type does not exist. in web/core/lib/Drupal/Core/Entity/Sql/SqlCo
ntentEntityStorage.php:761
  ╳  Stack trace:
  ╳  #0 web/core/lib/Drupal/Core/Entity/EntityBase.php(347): Drupal\Core\Entity\Sql\SqlContentEntityStorage->delete()
  ╳  #1 web/core/modules/user/user.module(691): Drupal\Core\Entity\EntityBase->delete()
  ╳  #2 web/core/includes/batch.inc(295): _user_cancel()
  ╳  #3 web/core/includes/form.inc(955): _batch_process()
  ╳  #4 vendor/drupal/drupal-driver/src/Drupal/Driver/Cores/Drupal8.php(201): batch_process()
  ╳  #5 vendor/drupal/drupal-driver/src/Drupal/Driver/DrupalDriver.php(111): Drupal\Driver\Cores\Drupal8->processBatch()
  ╳  #6 vendor/drupal/drupal-extension/src/Drupal/DrupalExtension/Context/RawDrupalContext.php(266): Drupal\Driver\DrupalDriver->processBatch()
  │
  └─ @AfterScenario 

So, that's helpful.

IEF tests are all passing. So presumably this has something to do with Conditional Fields.