Remove ETag middleware to disable ETag for all requests

[aduth]

🛠 Summary of changes

Removes the default Rack ETag middleware to avoid generating an ETag response header.

Benefits:

• Improve performance by avoiding creating a body digest for each request
• Shrink size of response
• Consistent with expectation that all routes are not to be cached (source)
• Avoid ad-hoc usage (example)

📜 Testing Plan

1. curl -I http://localhost:3000
2. Observe there is no ETag response header