feat: exposes baseline metrics

[saltiyazan]

Description

• Exposes basic Go metrics on the Metric endpoint
• Adds a test case
• Improves configYaml struct to specify required keys

The solution creates a custom handler for the metrics endpoint, that handler will run for any collectors registered in the metrics registry, for now we only have the collector of some basic Go metrics, but this should be easy to extend in the future with custom collectors.

To test this, run the service and curl the /metrics endpoint.
To test this with prometheus, configure prometheus with the following job:

scrape_configs:
  - job_name: gocert
    scrape_interval: 10s
    static_configs:
    - targets:
      - localhost:443

Run prometheus then curl the metrics endpoint of prometheus, for example:
`curl http://localhost:9090/metrics | grep gocerts'

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[saltiyazan]

Converted to draft, figuring out why are unit tests failing

[gruyaume]

Looks good, the description should be adapted to the new approach (i.e. metrics are not under /api/v1.

I tested this locally and it looks good :)

[kayra1]

perfect. just one small thing.