Move the API to django-ninja

[fretchen]

We started the implementation of https://qlued.alqor.io/api/v1/docs. However, it would be good to finish the transition and depreciate the old way.

This will require to implement and test:

• "str:backend_name/get_config/"
• "str:backend_name/post_job/"
• "str:backend_name/get_job_status/"
• "str:backend_name/get_job_result/"
• "str:backend_name/get_next_job_in_queue/"
• "str:backend_name/get_user_jobs/"
• "/backends/"

[fretchen]

We will not move get_next_job_in_queue. This one is outdated and we will leave it inside for legacy reasons.
However, this is really no point in adding it again as sqooler was changed to pull the information directly from the storage.

[fretchen]

Decided to move #34 to the next milestone. So we can remove it here.