Additional parameter for copyAssetsFileIOS() to return image in HEIC format

This line here https://github.com/itinance/react-native-fs/blob/a67a8d7cc7b51fc7892cf5a345c62efe22054fde/RNFSManager.m#L831 ensures that the result obtained from copyAssetsFileIOS() is always in JPEG format.

It will be great if copyAssetsFileIOS() has an extra optional parameter to determine if the result should be in JPEG. In certain situations, it could be helpful if the original image format (e.g. HEIC) were returned instead. For example, image backup in HEIC format would be more space efficient.