Move optional config to submodule, since it installs automatically.

Problem/Motivation

Thanks for this module, works great.

Linkit installs a default profile and image style that by itself is innocuous, but does clutter up the database/configuration and is unnecessary for the module to function.

Deleting the config is possible, but shouldn't necessary in the first place.

Steps to reproduce

Install linkit
See default configuration.

Alternatives I've considered

Run
drush cdel image.style.linkit_result_thumbnail
drush cdel linkit.linkit_profile.default

But I can't do this on sites I don't have access to, but do use my installation profile.

I could also write an update to delete the config

\Drupal::configFactory()->getEditable('image.style.linkit_result_thumbnail')->delete();
\Drupal::configFactory()->getEditable('linkit.linkit_profile.default')->delete();

But why?

Proposed resolution

Create new submodule with the example configuration.

Remaining tasks

Create new submodule with the example configuration.

User interface changes

Need to install submodule if you want the example config

API changes

None
This will not affect existing installations.

Data model changes

None