#1611 Allow disabling Shotover metrics

[justinweng-instaclustr]

This PR makes the field observability_interface optional in configuration.yaml. The Shotover metrics reporting will be disabled when this field is not specified.

A test function has been added to verify Shotover can still process Redis requests with metrics disabled. As discussed with @rukai, we don't need to check that querying the prometheus endpoint returns the error of connection refused because the endpoint address is not specified at all.

Closes #1611

[codspeed-hq]

CodSpeed Performance Report

Merging #1655 will not alter performance

_{Comparing justinweng-instaclustr:1611-allow-disabling-metrics-reporting (4a1182d) with main (f8dfaac)}

Summary

✅ 37 untouched benchmarks

[rukai]

LGTM!
Good thinking to update the docs.