GitLab

* [doc] add checkpoint related docstr for booster

* [doc] add en checkpoint doc

* [doc] add zh checkpoint doc

* [doc] add booster checkpoint doc in sidebar

* [doc] add cuation about ckpt for plugins

* [doc] add doctest placeholder

* [doc] add doctest placeholder

* [doc] add doctest placeholder

* [doc] add en booster plugins doc

* [doc] add booster plugins doc in sidebar

* [doc] add zh booster plugins doc

* [doc] fix zh booster plugin translation

* [doc] reoganize tutorials order of basic section

* [devops] force sync to test ci