[API] Openapi documentation in multiple proxy situations

[fjugipe]

We need to enable a possibility for correct formulation of the API documentation when accessing it through a proxy.

Currently the API tries to load openapi.json from /openapi.json which does not work when accessing the API through a proxy i.e. https://example.proxy.com/e-soh/docs. In this scenario the /openapi.json request is forwarded to https://example.proxy.com/openapi.json and results to 404 or returning the proxys /openapi.json if there is one.

In this case also the server to be queried for the endpoints in swagger should be dynamically generated depending on which route the user is accessing the API.