portable: honor --force for directory extensions

portable: honor --force for directory extensions

Pass relax_extension_release_check through the directory extraction
path instead of hardcoding false. Directory extensions now honor the
same --force relaxation as dissected images.

Reproducer:
  cp -a /tmp/app0 /tmp/app10
  sudo portablectl attach --force --runtime \
      --extension /tmp/app10 /tmp/rootdir app0

Before:
  directory image extraction always used strict extension-release name
  checks. --force relaxed other extension paths but still rejected a
  renamed directory extension with matching metadata.

Follow-up: 06768b90a32ac0d36252ebc5f426ad471bf29fce