Specifying auth_scope for services (caldav, carddav)#45

Hi, first of all thanks for all the work you've put into this project! I've recently switched from `mailctl` to `oama` and I am struggling with defining caldav and carddav scopes to be authed with. With `mailctl` it was possible to create `services.yml`, such as: ``` google: ... auth_scope: https://mail.google.com/ https://www.googleapis.com/auth/carddav https://www.googleapis.com/auth/calendar ``` and then use the obtained tokens with utils like [vdirsyncer](https://github.com/pimutils/vdirsyncer). In `oama` the scope seems to be [hardcoded in config](https://github.com/pdobsan/oama/blob/main/lib/OAMa/Environment.hs#L80). Or maybe it can already be set via the config file but I missed how to do it?