Enable Organic groups on media types

I wonder if there's a better way of doing it with BundleEntityFormBase rather than specifically hardcoding for MediaTypeForm?

A smaller PR.

I had to remove the instanceof check from Drupal\og_ui\BundleEntityFormAlter::formAlter(array &$form, FormStateInterface $form_state): void

In order to make patch #3 work.

    if (!$form_state->getFormObject() instanceof BundleEntityFormBase) {
      throw new \InvalidArgumentException('Passed in form is not a bundle entity form.');
    }
    static::prepare($form);

I'm pretty sure this check has a purpose but it was preventing showing the checkbox for media entities in my case.