Add permissions to EC2 to describe running Fargates

[aloftus23]

🗣 Description

Add permissions to describe Fargate asks to the EC2 instance.

💭 Motivation and context

The EC2 is the control center that launches the SQS and Fargate scan process. With scans that require limited API access (limited number of running containers), we need to make sure there aren't any existing containers for each scan so we don't go past the limit of concurrent containers per scan.

With these permissions we can check before launching.

🧪 Testing

Passes terraform plan nad formatting.

✅ Pre-approval checklist

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

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Create a release.

[nickviola]

LGTM