(Discontinued) Show error logs in embedded sub-command

[wxiaoguang]

Partially resolves:

• embedded subcommand not working in Linux #12082

Before: if Fatal error occurs, users see nothing, Gitea exits.
Now: If Fatal error occurs, users can know what happened.

There are still many flaws in Gitea setting system, some fatal errors during CLI sub-commands can be:

• ...s/setting/setting.go:954:loadFromConf() [F] Expect user 'xiaoguang' but current user is: sysop
• ...s/setting/setting.go:962:loadFromConf() [F] Gitea is not supposed to be run as root. Sorry. If you need to use privileged TCP ports please instead use setcap and the cap_net_bind_service permission
• ...s/setting/setting.go:799:loadFromConf() [F] Failed to create '/nonexistent/.ssh': mkdir /nonexistent: permission denied

That's very unfriendly to users and stops embedded sub-command, the Gitea setting system should be polished more, that's what I mean "partially resolves".

[wxiaoguang]

I need think and test more. Give me some more time on this.

[wxiaoguang]

Discontinued, feel free to take it or make a new PR.