feat: allow user to set TOC display preference (#6943)

Co-authored-by: Tom Moor <tom.moor@gmail.com>

shared/constants.ts

@@ -1,4 +1,5 @@
 import {
+  TOCPosition,
   TeamPreference,
   TeamPreferences,
   UserPreference,
@@ -22,6 +23,7 @@ export const TeamPreferenceDefaults: TeamPreferences = {
   [TeamPreference.PublicBranding]: false,
   [TeamPreference.Commenting]: true,
   [TeamPreference.CustomTheme]: undefined,
+  [TeamPreference.TocPosition]: TOCPosition.Left,
 };
 
 export const UserPreferenceDefaults: UserPreferences = {