Add ability to indicate which post a question is a duplicate of

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So just now I came across this question, which appears to be a duplicate of this question.

I saw that I had the ability to close the question, so I did so, marking it as a duplicate.

However, I notice that there is no way to indicate which post the question is a duplicate of. If you visit the duplicate question, all it says is that the question was closed because it is an exact duplicate.