Feat: add entry for jihu to override discover link

What does this MR do and why?

Background

Jihu needs to replace the link with something else, but right now it is hard-coded so it can not be changed very easily.

Strategy

The current link described on the discover page is hard coded and it is hard to replace it in normal ways, so I extracted it from the template and created a dedicated file for exposing the entry of the link.

In the template, we import from jh (when Jihu enabled), or ee (when not a Jihu instance).

/cc @prajnamas @orozot @qk44077907

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