feat: adds more standard compliant request body handling

[daniel-white]

Addresses #2255

Summary

• removes Content-Type as a detection mechanism for request bodies
• adds more detailed error when the proxy detects a request body in a GET/HEAD request, which node-fetch does not support

Checklist

• The basics
  • I tested these changes manually in my local or dev environment
• Tests
  • Added or updated
  • N/A
• Event Tracking
  • I added event tracking and followed the event tracking guidelines
  • N/A
• Error Reporting
  • I reported errors and followed the error reporting guidelines
  • N/A

[EdVinyard]

Other than a single question for my own curiosity, this looks good to me.

[EdVinyard]

I've never tried to do this before. Does '{}' get serialized to a zero-length request body?

[daniel-white]

yea - its a verbatim string here - so the request body is just {}