Clean up P&E's SQS process

[aloftus23]

🗣 Description

Clean up the P&E SQS process. The old flow is described in this PR.

Instead of using ECS services to manage concurrent Fargate tasks, we can simply generate Fargate tasks through "ECS Run tasks". The issue with ECS services is that you can set a desired count of concurrent tasks (say 10), but if one finishes the script early, it will start a new one even though there's nothing left to run. We want tasks to complete and then shut down, which ECS run task ensures.

Also, this method removes the need of a "Control" SQS queue that parses messages into scan specific queues. Now we only need a scan specific queue.

💭 Motivation and context

Save costs and time running scans through SQS, lambda, and Fargate.

🧪 Testing

Tested locally and passes checks.

📷 Screenshots (if appropriate)

OLD:

NEW:

✅ 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.

[rapidray12]

I am not a fan of magic numbers (e.g. 604200). We need to clean those up. Also we need to come up with a new acronym. Maybe switch from PE to XFD