core: method to know if a profile/entity is an admin: the new `is_admin` SatXMPPEntity property tell if it's an administrator. Admin JIDs are retrieve on init, so they can be looked after when profle is not available (notably when a component handle a request and has only a JID available). The new `memory.isAdminJID` method is then used.

version: "3.6"
services:

  prosody:
    image: libervia/prosody:demo
    build: prosody-demo

  backend:
    image: libervia/backend:dev-demo
    build: backend-dev-demo

  web:
    image: libervia/web:dev-demo
    build: libervia-web-dev-demo