Document package differences between variants

[rpkelly]

What I'd like: In a discussion it was brought up that is is not documented that Bottlerocket baremetal variants do not contain the aws-iam-authenticator package. I'd like to see documentation detailing the differences between the packages and features available in each variant.

Any alternatives you've considered: Add what variant each package is in to the documentation created for #14

[stockholmux]

This is a really good idea, although I think we have to tackle #14 first.