feat: Custom electronDist callback

[mmaietta]

Follow up from discussion with @lutzroeder and @quanglam2807
#5481 (comment)

• Enabling electronDist to be a function that returns the path to the electron dist directory.
• Updated documentation for the expected options (string path vs function)

This is necessary for universal builds where an electronDist must be specified per-architecture and there are multiple Arch-Targets provided. This applies to Windows (ia32+x64) and Mac (x64+arm64)

const archs = platform === builder.Platform.MAC ? [builder.Arch.universal] : [builder.Arch.x64, builder.Arch.ia32]
const targets = platform.createTarget(null, ...archs)

Used in electron-builder config as::

electronDist: (options: PrepareApplicationStageDirectoryOptions) => {
    // console.log("PrepareApplicationStageDirectoryOptions", options)
    return prepareRebrandedElectronDist(options);
},

Note: this does not change the functionality of what electron-builder searches for at that path: search for properly-named zip OR assume it as unpacked app directory. This only allows an alternative way of specifying where those files are located.