feat: Implement Prometheus metrics exposure in SmartMetrics

- Added Prometheus gauges for CPU and memory metrics.
- Implemented HTTP server to expose metrics at /metrics endpoint.
- Created methods to enable and disable the Prometheus endpoint.
- Updated getMetrics() to set gauge values.
- Added tests for Prometheus metrics functionality.
- Updated documentation plan for Prometheus integration.

ts/smartmetrics.interfaces.ts

@@ -1,4 +1,3 @@
-// this might be extracted into a package @pushrocks/smartmetrics-interfaces in the future
 export interface IMetricsSnapshot {
   process_cpu_seconds_total: number;
   nodejs_active_handles_total: number;