Add unit test to ensure config description links include target

[valarnin]

All links in config descriptions should open in a new window, via target="_blank" in the <a> tag.

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Unrelated to this PR, but I wonder if we should have a unit test that makes sure <a> tags in config comments includes target="_blank"?

Originally posted by @valarnin in #1080 (comment)

[Bing-su]

https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/a#target

Here is the official definition for that.

Personally, I think it's necessary.