Manually approve new registration (#13083)

Manually approve new registration (#13083)

* Add register manual confirm settings option

The new settings option is used when manually approving new
registrations.

* Enable manual confirmation of new registered user

When manual registration confirmation is desired (by default `false`)
create new user in the database that is *not active*. The user must then
be activated manually.

This change speeds up the process of adding new confirmed users for
Gitea instances without external auth mechanism. (Currently the option
is to manually create new user by admin.)

* Update docs/content/doc/advanced/config-cheat-sheet.zh-cn.md

Co-authored-by: a1012112796 <1012112796@qq.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: a1012112796 <1012112796@qq.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>