Clean-up SQS code and fix visibility timeout

[aloftus23]

🗣 Description

This PR:

• Cleans SQS code by removing unnecessary variables (i.e. Queue specific variables - can use generic instead)
• Fixes containers picking up the same message: Increase visibility timeout to 5 hours (once a message is read, it won't be visible to be picked up again for 5 hours instead of 5 minutes)
• Fixes Shodan to use different API keys for each container
• Updates readme

💭 Motivation and context

Bug fixes and improve ease of adding new scans.

🧪 Testing

Tested locally and passes checks

✅ 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

[schmelz21]

LGTM