Adapt code against Drupal standards

config/install/vk_entity_identifier.settings.yml

src/Controller/VkEntityIdentifierController.php

src/TwigExtensions/VkEntityIdentifierTwig.php

src/VkEntityIdentifier.php

src/VkEntityIdentifierFieldManager.php

vk_entity_identifier.install

vk_entity_identifier.module

vk_entity_identifier.permissions.yml

vk_entity_identifier.routing.yml

vk_entity_identifier.services.yml