new auth flow implementation from new design

[yokwejuste]

From the new auth flow provided on the design we should implement some changes on the backend to match all this data.

[NdibeRaymond]

For this I think on the backend we need to change two files (maybe three or more if you add comment changes):

1. zubhub_backend/zubhub/creators/serializers.py
   CustomRegisterSerializer:

   • add tag field
   • validate the tag received

2. zubhub_backend/zubhub/creators/adapter.py
   CustomAccountAdapter

   • get the tag string, get the corresponding creatortag here and set it
   • if creatortag is staff you need to set creator.is_staff = True too
   • do these before creator.save()

do not touch the tasks.py or signals.py since The CreatorTag operation in signals just helps to make sure that when you create a user without specifying a CreatorTag (or somehow remove all of a creators tag) it defaults to "creator"

Also you might need to update RegisterCreatorAPIView top comment by adding the tag field there.

[coderatomy]

Related to #1021