[Feature]: Enhance metrics and observability

[LorenzoTettamanti]

Is your feature request related to a problem?

• Yes

  Problem Description:

  Currently cortexflow does not have an extensive support for metrics and observability. This issue aims to track the progress of the observability.

  Supported metrics:
  - DNS_REQUEST
  - DNS_RESPONSE_TIME

  Solution:

  Add:
  - Request per second
  - Latency metrics
  - % of failed requests
  - % of accepted requests
  - mean response time