Rename Rack Attack log field: request_method -> method

What does this MR do and why?

method is what is used in the API and controller logs. Keeping this the same makes it easier to filter for logs properly.

References

Relates to gitlab-com/gl-infra/production#19438 (comment 2385407012)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Enable Rack Attack: in /admin -> Settings -> Network, check Enable unauthenticated API request rate limit, and click Save.
2. Be careful: lower the limits of unauthenticated API requests to a low value (e.g. 5). Note that this might lock you out. 😄
3. gdk restart rails-web for the limits to take effect.
4. Hit curl http://gdk.test:3000/api/v4/users at least N times.
5. Check log/auth_json.log:

  "severity": "ERROR",
  "time": "2025-03-07T19:54:15.246Z",
  "correlation_id": "01JNS2RDQVMXXCTZBNTZQ88DSH",
  "message": "Rack_Attack",
  "env": "throttle",
  "remote_ip": "127.0.0.1",
  "method": "GET",
  "path": "/api/v4/user",
  "matched": "throttle_unauthenticated_api",
  "status": 429,
  "redis_calls": 2,
<snip>

5. Disable Rack Attack.