Reduce boilerplate for API handlers #9
Description
There is a lot of boilerplate code in cmd/api/main.go for declaring and implementing API endpoints, and a lot of it is doing the same thing.
Consider ways to reduce the repetition here. Bonus points if you can make it declarative!
This could align well with a task for generating client code for calling the API, which will prove useful once we start implementing a frontend for OpenAtlas. Do Protobufs and gRPC make sense here? How does that, or any other solution, align with the usage of JSONAPI? Can we generate both useful client and server code?