feat(agents): address killswitch usability issues

[lattejed]

Motivation

Killswitch is functional but takes too long to configure. Configuration should be handled automatically and require only local AWS credentials to run.

Solution

• AWS credentials are sourced locally from a well known location
• All secrets are fetched from an S3 bucket
• Adds an --environment flag to select deployment to target (e.g., production)
• The kill process now runs in parallel to be faster
• Has a required --force flag (the opposite of a --dry-run flag)
• Output is human-readable and more descriptive (no longer json)

PR Checklist

• [x] Added Tests
• [ ] Updated Documentation
• [ ] Updated CHANGELOG.md for the appropriate package
• [x] Ran PR in local/dev/staging