WIP: Generic ArrayMap

[carolynvs]

What does this change

Not sure if we'll actually do this. I updated SourceMapList to ArrayMap (naming is hard!) and saw just how much would be impacted by changing the data structure from a slice to a map.

What issue does it fix

Nothing, Aaron nerd sniped me 😅

Notes for the reviewer

N/A

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR