How to properly manage field types for a content type created by a module?
To properly manage fields added by a module, so that a field is added and removed when the module is installed and uninstalled, add an enforced dependency for your own module to the yaml file:
/config/install/field.storage.node.field_example.yml
...
dependencies:
  enforced:
    module:
      - mymodule

See https://www.drupal.org/node/2404447