Render specific openapi for the running instance of the sms.

This MR changes the openapi json, so that we only include the instance that currently runs the sms. This has the advantage that we only provide the login mechanism that is associated with this specific instance. (So no need for the user to select the only one that works with the instance).

It also refactors a little bit how the data from the well known url are extracted (in order to have one single middleware that then sets the variables into the app config).