Add Convex Hull in C++

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To request a new code snippet, please fill out the following:

Project name: Convex Hull Project link: https://sampleprograms.io/projects/convex-hull Language: C++

The project link must be a link to a project on the Sample Programs Website project list. If you would like to add a new project to the Sample Programs Website, please first make a pull request to the Sample Programs Website.