Update the workplace services to make the username property used when calling the API configurable
Currently, we rely on the OIDC subject
property in the user profile (https://git.xwikisas.com/xwikisas/swp/xwiki/-/blob/beb039aea054a83efef2b1f987bf25ff41bfd30a/extension/workplace-services/api/src/main/java/com/xwiki/projects/swp/workplaceservices/internal/WorkplaceServicesAPI.java#L131). The idea of this feature would be to expose a configuration variable to select which property should be used for contacting the API.
The property in question could be stored in another object, different from the OIDC object we use today. As such, the configuration should allow selecting the class of the object that holds the property.