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.

[DEFAULT]
xmpp_domain = server1.test
email_server = libervia-backend.test
email_port = 8025
email_admins_list = admin@server1.test

[component file-sharing]
http_upload_public_facing_url = http://localhost:7777
http_upload_connection_type = http
http_upload_port = 7777