Set the scope in search context from group issue and MR pages

What does this MR do?

This is related to #287921 (closed)

It seems to me the controller name is always groups when selecting issues or merge requests in a group. So, in this case, I have to use action name to identify the scope and set the scope parameter in the form according.

I also added specs for both ruby and haml code changes.

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Related to #287921 (closed)