Issue #3529874: Create `drupal_nl` config split.
- Replaced default configs with
la_eu
default configs. - Created
drupal_nl
config split. - Extracted la_nl-specific configs into
drupal_nl
config split. - Installed missing modules.
- Created empty
la_eu_default_content
module. - Added
config-split.md
doc.
Closes #3529874