fix(plex): do not fail to import Plex users when Plex Home has managed users (#1699)

* fix(plex): do not fail to import Plex users when Plex Home has managed users

* fix: default display name to email when user has no username

also, do not set username or plexUsername when it is the same as the user's email address

* fix(ui): user display name placeholder should reflect fallback logic if username is not set

* fix(ui): hide email addresses of other users if logged-in user does not have Manage Users permission

* fix: always set Plex username even if same as user's email

* fix: remove unnecessary permission check

* fix: transform email addresses to lowercase

src/components/UserProfile/UserSettings/UserGeneralSettings/index.tsx

@@ -188,7 +188,9 @@ const UserGeneralSettings: React.FC = () => {
                       id="displayName"
                       name="displayName"
                       type="text"
-                      placeholder={user?.displayName}
+                      placeholder={
+                        user?.plexUsername ? user.plexUsername : user?.email
+                      }
                     />
                   </div>
                   {errors.displayName && touched.displayName && (