Support fetch released docs from main repo (#775)

Support fetch released docs from main repo (#775)

* Support fetch released docs from main repo

All our history docs before we migrate doc to apache/dolphinscheduler
is in apache/dolphinscheduler-website branch `history-docs`.

After we migrate doc to apache/dolphinscheduler we have two ways to
handle its release docs, one of the ways is copy-paste docs from
apache/dolphinscheduler to apache/dolphinscheduler-website branch
`history-docs`, the other way is to find some black magic fetch docs
based on the release tag.

Of cause, we prefer to choose the second way. Fetch base on released
tags.

* rename bash script from release.conf.sh to conf.sh

* Change fetch branch instead of tag

* fix