Implement `rcodesign` support for code signing on Linux

[iameli]

Recently Streamplace has been able to move almost all of our Mac building over to Linux containers thanks to the apple-codesign Rust package, AKA the rcodesign command-line tool. This has saved us money on Mac builders and made our builds faster.

Unfortunately we still have a dependency on a Mac builder for our Electron app due to this package only supporting native Mac codesigning. It would be amazing if electron-osx-sign implemented rcodesign support! Would be very helpful.

(We're stuck with macOS in CI for the foreseeable future for our iOS builds... but maybe that can change too someday!)

[insraq]

I have been working on signing and notarizing of CivIdle (https://github.com/fishpondstudio/CivIdle/) for macOS build. I first attempted to implement rcodesign for this package, but this package has a big API surface is quite coupled with Apple's codesign and rcodesign is not really a drop-in replacement. Lots of complications lie in getting certificates and providing API keys. In the end, I decided to skip osx-sign completely and use rcodesign command line to sign and notarize the app, which works well but needs several ugly hacks. If you are interested in the solution, take a look at the script here:
https://github.com/fishpondstudio/CivIdle/blob/70bafee42c51b37669c153f65086e4e30ff76b18/build/ReleaseElectron.js#L61

[iameli]

I have been working on signing and notarizing of CivIdle (https://github.com/fishpondstudio/CivIdle/) for macOS build. I first attempted to implement rcodesign for this package, but this package has a big API surface is quite coupled with Apple's codesign and rcodesign is not really a drop-in replacement. Lots of complications lie in getting certificates and providing API keys. In the end, I decided to skip osx-sign completely and use rcodesign command line to sign and notarize the app, which works well but needs several ugly hacks. If you are interested in the solution, take a look at the script here: https://github.com/fishpondstudio/CivIdle/blob/70bafee42c51b37669c153f65086e4e30ff76b18/build/ReleaseElectron.js#L61

Oh awesome, thank you! That'll probably get the job done.