feat: electron builder binaries base url from env

[okmiim]

Added function to get the base URL for GitHub (electron-builder-binaries) using environment variables used by electron-builder (https://github.com/electron-userland/electron-builder/blob/f3404d32f029dfb63e83067012f15ef67838f326/packages/app-builder-lib/src/binDownload.ts#L21-L25).
This could also be extended in a similar way for "ELECTRON_BUILDER_BINARIES_CUSTOM_DIR".
The implantation is not tested, however it is structured the same way as

app-builder/pkg/electron/electronDownloader.go

Lines 84 to 99 in 7e03397

	func getBaseUrl(config *ElectronDownloadOptions) string {
	v := os.Getenv("NPM_CONFIG_ELECTRON_MIRROR")
	if len(v) == 0 {
	v = os.Getenv("npm_config_electron_mirror")
	}
	if len(v) == 0 {
	v = os.Getenv("ELECTRON_MIRROR")
	}
	if len(v) == 0 {
	v = config.Mirror
	}
	if len(v) == 0 {
	v = "https://github.com/electron/electron/releases/download/v"
	}
	return v
	}

and should work without any problems.