Provide API key via parameter

[samuelmeuli]

Thanks for this package!

It would be nice if the user could provide the API key (the content of the .p8 file) as a parameter to the notarize function instead of having to store it as a file. Internally, electron-notarize could temporarily write the key to disk and remove it after completing the notarization.

@MarshallOfSound Is this something you'd be willing to consider? :)