Allow session cookie options to be customised

Closes #4717

packages/node_modules/node-red/settings.js

@@ -133,6 +133,7 @@ module.exports = {
  *  - httpServerOptions
  *  - httpAdminRoot
  *  - httpAdminMiddleware
+ *  - httpAdminCookieOptions
  *  - httpNodeRoot
  *  - httpNodeCors
  *  - httpNodeMiddleware
@@ -178,6 +179,11 @@ module.exports = {
     //    next();
     // },
 
+    /** The following property can be used to set addition options on the session
+     * cookie used as part of adminAuth authentication system
+     * Available options are documented here: https://www.npmjs.com/package/express-session#cookie
+     */
+    // httpAdminCookieOptions: { },
 
     /** Some nodes, such as HTTP In, can be used to listen for incoming http requests.
      * By default, these are served relative to '/'. The following property