Make all fields a tuple in serializers

[kevinetienne]

If in a project we define a tuple of core fields and try to concatenate them with the original serializer fields we need to add an exception to RegistrationSerializer.

Making all fields a tuple allow to subclass them more easily.

[meshy]

I also like this, as it stops changes to the fields from accidentally propagating up the tree of subclasses.

[kevinetienne]

Ready for review/merge. Not sure if it was a breaking change but it looks like project sub-classing RegistrationSerializer.Meta.fields might get an error (when concatenated with something other than a tuple).

[meshy]

@KevinEtienne I agree, frustrating as it is, I think this does count as a breaking change. It might be worth expanding on the changelog to briefly explain how to migrate to this version.

[kevinetienne]

Cool thanks, I'll do that

[kevinetienne]

Updated, @Ian-Foote @adam-incuna can you review/merge please?

[adam-thomas]

:+1:

[kevinetienne]

Thanks :)