Disclaimer at app store.

Created by: VioZhang

Add a description of risk warning and the way to get support when downloading app from app center. Inform the user the risk about the app downloaded from the app store. After legal verification，we have the description in Chinese as follow “（1）您会遵守该软件的开源协议； （2）您下载并安装该软件导致的任何后果将由您自行承担。 如果需要相关支持服务请联系KubeSphere.cloud”.

The drawing design ：https://www.figma.com/file/ME6F2CvFfiXLcmnCriA3s7/Uncategorized-Requirements?node-id=2%3A529

/cc @kubesphere/sig-console /cc @Patrick-LuoYu /kind feature-request