bug(ros): fix license conversion between package.xml and SPDX standard.

[ruben-arts]

Currently, the package.xml doesn't have the exact same format as SPDX. As rattler-build expects that we should write a converter instead of just adding nothing or any other file and name for the license.

[ruben-arts]

Searching for License usage in the package.xml in GitHub: https://github.com/search?q=path%3Apackage.xml+%3Clicense%3E&type=code&p=2

I think we should try to make an option in rattler-build to just throw huge warnings but allow the usage of wrongly defined licenses.

Because I don't want to be responsible for wrongly mapping them, and I don't want people to get stuck on horrible errors if they use someone else ROS package that wasn't pixified yet.

[baszalmstra]

This was merged in vinca, I think we should handle this the same in our backend.