Introduce Metrics-tracking / Telemetry

[yenicelik]

We have logging to stdout through tracing which uses anysc tokio under the hood. We want something similar that we can hook up to Prometheus or Grafana to show analyzed data. For this we can use https://github.com/open-telemetry/opentelemetry-rust

Amongst others, following items should be tracked (please edit this issue as more items come to mind):

• [ ] cpu utilization
• [ ] api calls (per second)
• [ ] how many extractors are running
• [ ] how many executors are running
• [ ] how often the scheduler is invoked
• [x] Counters on API requests
• [x] Latency of api requests
• [x] Latency and counters of DB calls.
• [x] Latency and counters of extractor calls in the executor.

common system-level information:

• https://opentelemetry.io/docs/specs/otel/metrics/semantic_conventions/process-metrics/

[yenicelik]

Addressed partially by https://github.com/diptanu/indexify/pull/123 metrics like disk usage, CPU usage, context switches are missing