Say tenants are Enterprise only where the installation asks, as the demo will

On a server that is not Enterprise the Tenants page is still only the
notice. On Enterprise the notice is gone -- a real installation that has
tenants has the licence -- unless SHOW_ENTERPRISE_NOTICES=1 asks for it above
the list. The public demo will set it: it reports Enterprise so tenants can be
shown, and should not suggest they come without the licence. The setting
reaches the browser as session.ihasmail.server.enterpriseNotices.

web/src/jmap/types.ts

@@ -40,6 +40,8 @@ export interface JmapSession {
       edition?: string | null;
       /** Where Stalwart's own administration is (STALWART_ADMIN_URL), for a session that may administer. */
       adminUrl?: string | null;
+      /** SHOW_ENTERPRISE_NOTICES: an Enterprise-only section says so even on Enterprise. */
+      enterpriseNotices?: boolean;
     };
     /**
      * False when this session may not administer: the operator turned it off,