Fix help page redirect 404 when set `Documentation pages URL` to origin

What does this MR do and why?

Related Issue: #1835 (closed)

原先JH会强制把所有help page都指向jh/xxx/xxx的path，导致配置了Documentation pages URL为官网英文help地址时原本需要/ee/xxx/xxx才能访问的页面404。产品提出需要只fix配置了docs.gitlab.com后能正确访问官网英文help，且该配置系统内无其它功能涉及引用，所以就做了一个快速修复。

Screenshots or screen recordings

before：

after:

Related to #1835 (closed)