vcpkg create github template

[vpaladino778]

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Is your feature request related to a problem? Please describe.
Right now, the vcpkg create command only creates a template if your using a direct .zip download link. There exists no template for a github portfile.

Proposed solution
When the vcpkg create command is called, it will check if its a github.com url. If it is, instead of using the scripts/template/portfile.in.cmake template, it will use a new file, scripts/template/portfile_github.in.cmake which will contain a simple github portfile solution.

Additional context
I posted this issue because I want to implement this myself. I wanted to get the input/suggestions of the Microsoft employees that maintain the repository before I go start working on it. Let me know if this is something worth working on.

[PhoebeHui]

For me, It's good to extend current template, however, I'm not sure if it's necessary to create a separate portfile_github.in.cmake, since they have many same functions such as vcpkg_configure_cmake, vcpkg_install_cmake, vcpkg_fixup_cmake_targets, and handling copyright, and other common variables.

[vpaladino778]

@PhoebeHui Thanks for your reply! I figured a github specific one would be better so we could use vcpkg_from_github instead of vcpkg_download_distfile (Instead of making the user manually delete the unnecessary one out). If we made a few adjustments to vcpkg create for github, it could be create a nearly complete portfile for simple github packages. Maybe it's a nonissue, just something i was thinking about.

[JackBoosY]

If anyone have interest with this, please handle my PR #9430.