Add option for copying keys into Info.plist on MacOS

[mikayla-maki]

Hello!

We're building a local app and need to add some additional keys into our Info.plist for requesting access to system services like the microphone. So I decided to take a crack at implementing #33 for MacOS.

Current implementation is simple:

• It adds a osx_info_plist_exts field into the bundle settings,
• It reads each file in that path, and blindly appends it's contents into the Info.plist file, after cargo-bundle has generated it's keys but before it closes the <dict> and <plist>.

I haven't written documentation for this yet, as I imagine folks here will have some thoughts on the name and behavior for this.

Let me know what you think!

[9mm]

This would be awesome, because I really need CFBundleDocumentTypes

[ActuallyHappening]

Did you use https://docs.rs/plist/latest/plist/?
Might make implementations a little better idk

[n1ght-hunter]

any chance this could be merged.
looking to use this functionality

[hacknus]

Would be great if this could be merged, I also need to use CFBundleDocumentTypes