List licenses of dependencies for binary releases

[clehner]

For distributing DIDKit in applications and for publishing it to non-native package managers, we should include a list of the dependency licenses and copyright notices. License info of cargo dependencies may be gathered e.g. using cargo-about, cargo-license, or cargo-lichking, or by parsing the output of cargo tree or cargo metadata. This could be added to a text file that would be included in the didkit npm package and flutter/dart plugin. Also, NOTICE files from dependencies using Apache License, Version 2.0 should be collected and added as required by the Apache license, maybe semi-manually since there are not many of these. Also, we should probably include licenses for Rust core (libstd, etc.), but is a little unclear how to do this currently: rust-lang/rust#67014