pm-4.1.x-dev/modules/pm_epic/pm_epic.install

<?php

/**
 * @file
 * PM Epic install file.
 */

use Drupal\Core\Field\BaseFieldDefinition;

/**
 * Install "summary" field on "PM Board" and "PM Board Column" entities.
 */
function pm_epic_update_94001() {
  $field_storage_definition = BaseFieldDefinition::create('string_long')
    ->setLabel(t('Summary'))
    ->setDescription(t('A short description in plain text.'))
    ->setDefaultValue('')
    ->setRequired(FALSE)
    ->setDisplayOptions('view', [
      'label' => 'visible',
      'type' => 'basic_string',
      'weight' => 5,
    ])
    ->setDisplayOptions('form', [
      'type' => 'string_textarea',
      'weight' => 5,
      'settings' => ['rows' => 4],
    ])
    ->setDisplayConfigurable('view', TRUE)
    ->setDisplayConfigurable('form', TRUE);
  \Drupal::entityDefinitionUpdateManager()
    ->installFieldStorageDefinition('summary', 'pm_epic', 'pm_epic', $field_storage_definition);
}