Enhance mutli-tenancy capabilities by adding configuration options at the organization level

We started experimenting with the multi-tenancy mode with the Belgium Federal State and a couple demands since then. It's particularly compelling for higher level administration that hold a service provider role towards lower level institutions. We think that adding a couple configuration options on the organization could make the multi-tenancy feature more usable. Here are a few ideas we had, so per organization one could enable or disable: - Social and SAML logins with different configuration - Sender's email address used for the platform's notification - Basic scss variable for styling - list to be completed.