Only allow json requests to the API after 0.17.0

[matmair]

We currently accept application/json, application/x-www-form-urlencoded and multipart/form-data on our API endpoints. I want to remove all options but json to streamline corner cases with encoding and reduce the schema.
I have not seen a valid use case that can not use json instead of the other 2.

Thoughts @inventree/triage @inventree/maintainer ?

[SchrodingersGat]

Don't we need multipart for uploading files? We have custom code in the react forms framework to accommodate this

[matmair]

My idea would be to only allow form-data on endpoints that need data upload - those should be reduced to a few for attachments and imports, so the API surface should still be reduced a lot (over half at least).