It's already possible to do that using the "site:" operator, but most people don't know about it.
It's also in Advanced Search-- which has become more and more difficult to find over the years. I'm glad I bookmarked it long ago as my default, because I honestly don't think I would ever stumble across it by accident today.*
* I went back and-- haha --searched. The link is at the bottom of the search-results page after you have already done a search. Who in the world does this? And who would think to look there, then? Normal places have "Advanced Search" as an option near their regular Search button.