Move AWS Authentication to How-To and Update Getting Started with Geodesic

[Gowiem]

what

• Updates Geodesic getting started to not be based around authenticated AWS CLI access, but around a super simple terraform project
• Moves AWS Auth + Geodesic to how-to article
• Fixes a couple issues with atmos getting started:
  • double "the"
  • api_key var still around even though we removed that code

why

• Simplifies Geodesic getting started and removes barrier to entry

[Gowiem]

@osterman two things:

1. I wasn't able to get terraform init -from-module to work with a subpath in the repository. I didn't try for that long as it seemed like that's some esoteric terraform init functionality which we don't need to use when git clone will do, but figured it was worth mentioning since we had originally discussed using that functionality.
2. I'm not exactly stoked with the example we've got here in regards to git clone, terraform apply, terraform output | jq .... It's simple, but obviously contrived yet again. Let me know if you have any additional thoughts on what we could do here to make it a more real world use-case.