Add a license to the packages and project

[agalbachicar]

I think it would be great to have an explicit license declaration in the packages. Not only the fields have a TODO, but that also provides a clear indication on your plans for the project.

For reference:

• https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository#choosing-the-right-license
• The ROS 2 community is used to use Apache 2, BSD 3-Clause and MIT among others.
• The parent pyads is licensed under MIT.

Thanks for considering it!