Add skip meta index command to generate appindex.json

[marcprux]

This PR adds a skip meta index command that will output an appindex.json file, containing a manifest of the app's metadata, including the localized fastlane information, relative links to the various icons and screenshots, and, optionally, embed the sbom (added in #227).

We also add an --appindex flag to skip export in order to include the metadata in exported builds, as well as link the appindex.json into the app's primary module's Resources/ folder so the app can introspect on its own metadata at runtime.