Plugin binding for `onServerStop` event

[junzhengca]

onServerStop can be quite useful, for example, you might want to close the server and do an automatic tarball backup to AWS S3.

It might be possible to use onServerInfo to achieve similar functionality as onServerStop, but that is quite hacky, a consistent API is more desirable.

[kafuuchino-desu]

yes its already in our developement plan, still, thanks a lot for your issue, and btw not only onServerStop will be added into pluginsV2,a lot more apis will be added such as onPluginReload etc