AWS: Check for or prevent changes to AWS resources from outside this project

[floehopper]

• Consider checking for or somehow preventing changes to the relevant AWS resources from outside this project, i.e. not via aws-cdk
  • See Detecting Unmanaged Configuration Changes to Stacks and Resources

[floehopper]

I think this is a bit of a nice-to-have, so I'm going to move this outside https://github.com/freerange/trello_backup/milestone/1.