Design restAPI specification

[ddelpiano]

• vfb-connect api to be mapped to rest endpoints 1 to 1
• use apicur.io

It is important to have a good understanding of the data model and api from #4 before completing this task. No need to be comprehensive in the apis, the most important and stable ones should be mapped accurately at this round.

After the apis are defined, they have to be used to generate the backend controller stubs with harness-generate.