Prometheus metrics export

[ri-nat]

I think, it would be great to have an optional (opt-in) ability to export some internal metrics in a Prometheus format. This could include metrics such as the number of connected WS clients, the number of requests processed, response time distribution, and so on.

This feature will be useful for those who run SurrealDB on-premise, especially those using Kubernetes, as Prometheus is a de-facto standard in that environment. However, to avoid adding any computational overhead for those who are not interested in capturing metrics, I propose that this option should be disabled by default.

If this is something that could be useful for SurrealDB, I can come up with a more detailed list of metrics for further discussion. Also, I'm interested in implementing this feature.