Switch to Rack::Attack for Throttling

[pglombardo]

Description

We've historically been using rack-throttle for request throttling. That gem has been deprecated in favor of rack-attack which this PR switches us to.

The change-over should be transparent for end users.

Related Issue

Type of Change

• [x] 📚 Examples / docs / tutorials / dependencies update
• [ ] 🔧 Bug fix (non-breaking change which fixes an issue)
• [ ] 🥂 Improvement (non-breaking change which improves an existing feature)
• [ ] 🚀 New feature (non-breaking change which adds functionality)
• [ ] 💥 Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🔐 Security fix

Checklist

• [ ] I've written tests (if applicable) for all new methods and classes that I created. (rake test)
• [ ] I've added documentation as necessary so users can easily use and understand this feature/fix.