feat: add license

[PaulFrambot]

License Workshop

[MerlinEgalite]

We should update all files

[QGarchery]

There are many files with the UNLICENSED keyword still. Those are test files and in the src/mocks folder too. Should they be GPL2 or MIT ?

[MerlinEgalite]

There are many files with the UNLICENSED keyword still. Those are test files and in the src/mocks folder too. Should they be GPL2 or MIT ?

I intentionally left them as UNLICENSED as it's does not really make sense to set a specific license to mock or test files IMO but I'm ok to change if you feel we should do it.

[QGarchery]

Yes I think it should be changed, it feels like it is an oversight otherwise and it's better if the rules are clear

[MathisGD]

I think that legally something unlicensed is equivalents to the most permissive ones, so why not just put that ?

Edit: no it is not, so we want something more permissive, just in case someone needs them for production use in some ways