Support using an API key for App Store Connect

[kohenkatz]

Now that API keys can be generated for App Store Connect, App Specific Passwords are deprecated.

altool has support for --apiKey and --apiIssuer arguments that can be used for this.

I would be happy to work on a PR, but I wanted to check if you are interested (or already working on it) before I start.

[thii]

We're not using this anymore but feel free to work on it if you have a use-case for it.