fix(prejoin,config) move hidePrejoinDisplayName to the prejoin section

config.js

     // Hides add breakout room button
     // hideAddRoomButton: false,
 
-    // Hides the participant name editing field in the prejoin screen.
-    // If requireDisplayName is also set as true, a name should still be provided through
-    // either the jwt or the userInfo from the iframe api init object in order for this to have an effect.
-    // hidePrejoinDisplayName: false,
-
     // Require users to always specify a display name.
     // requireDisplayName: true,
 
     //     // When 'true', it shows an intermediate page before joining, where the user can configure their devices.
     //     // This replaces `prejoinPageEnabled`.
     //     enabled: true,
+    //     // Hides the participant name editing field in the prejoin screen.
+    //     // If requireDisplayName is also set as true, a name should still be provided through
+    //     // either the jwt or the userInfo from the iframe api init object in order for this to have an effect.
+    //     hideDisplayName: false,
     //     // List of buttons to hide from the extra join options dropdown.
     //     hideExtraJoinButtons: ['no-audio', 'by-phone']
     // },

react/features/base/config/configWhitelist.js

     'hideConferenceSubject',
     'hideDisplayName',
     'hideDominantSpeakerBadge',
-    'hidePrejoinDisplayName',
     'hideRecordingLabel',
     'hideParticipantsStats',
     'hideConferenceTimer',

react/features/prejoin/functions.js

  * @returns {boolean}
  */
 export function isPrejoinDisplayNameVisible(state: Object): boolean {
-    return !state['features/base/config'].hidePrejoinDisplayName;
+    return !state['features/base/config'].prejoinConfig?.hideDisplayName;
 }
 
 /**