Create IAM user to enable ELK integration with AWS

🗣 Description

fixes #2536

Elk requires an IAM user with the permissions listed on the site below in order to integrate with our AWS account.

Also adds additional logging and removes unnecessary logic in scanExecution.

Passes pre-commit tests and terraform plan review.

[x] This PR has an informative and human-readable title.
[x] Changes are limited to a single goal - eschew scope creep!
[x] All future TODOs are captured in issues, which are referenced in code comments.
[x] All relevant type-of-change labels have been added.
[x] I have read the CONTRIBUTING document.
[x] These code changes follow cisagov code standards.
[x] All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
[x] Tests have been added and/or modified to cover the changes in this PR.
[x] All new and existing tests pass.