1. embed the lgx bundler into the flake.nix so directly calling nix build .#lgx gives us a lgx pakcage out of the box
2. Remove metada.json file in case cpp libraries
Remove module.yaml and use metadata.json exclusively for both runtime
and Nix build configuration. The nix block in metadata.json replaces
module.yaml for build-time settings. Updates all docs, skills, templates,
lib/*.nix files, and the waku-module-migrated example.
Iuri Matias