Detailed Subscription/`@live` and Defer/Stream usage data

We do not collect any usage data for subscriptions and `defer/stream`.

Instead of HTTP request duration, we can monitor average Subscription length.

Useful metrics to track:
- [x] ~~Number of subscriptions on a Subscription Root field~~
- [ ] Number of payloads sent/values published for a subscription root field
- [ ] Subscription connection duration/length
- [ ] Error rate while setting up a subscription on a subscription root field
- [ ] Error rate for published subscription payloads per subscription root field
- [ ] Protocol used for a subscription operation (WS, WS Legacy, SSE)