Add example module, or document how to make default_content_test installable

Problem/Motivation

It would be nice to offer a working example module. If you simply move default_content_test to the custom module folder and enable it, you get this feedback:

$ drush en default_content_test

In PreExistingConfigException.php line 65:
Configuration objects (field.storage.node.field_tags, taxonomy.vocabulary.tags) provided by default_content_test already exist in active configuration

If you delete the three YAML files in the /config/install folder you can install the module and the example content is created:

$ drush en default_content_test
 [success] Successfully enabled: default_content_test

Could default_content_test be tweaked into work as an example module as well, by removing the three YAML files in the /config/install folder, or are they required for testing, because tests are run against Minimal, and not Standard profile?

Alternatively a dedicated example module could be created ... or even simpler: Add the required steps to turn default_content_test into a working example under documentation. Something like this?

1. Move default_content_test into /modules/custom
2. Delete three YAML files in the /config/install folder
3. Remove line hidden: TRUE from default_content_test.info.yml (Optional)
4. Enable the module, and see that three nodes have been created under Content (/admin/content)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes