[FEAT]admin的server设置开关：Who can invite new users

[suhan1996]

Restrict Users from Inviting New Users Provide an option to restrict users from inviting additional users to avoid uncontrolled growth or unwanted additions to the platform.

加到server设置 Who can invite new users All users Admin only

前端可以隐藏对应的入口

[zerosoul]

如果走新增的扩展字段，设置成开关形式是最方便的，所以“曲线救国”了一下：把 Who can invite new users 改为 Only admin can invite users，默认关闭，开启则隐藏普通用户邀请入口。

已更新到 privoce.voce.chat