Add telemetry metric tests

[andrewlock]

Description

Adds a test for telemetry metrics. Currently only enabled for .NET, as I'm not sure what other teams have implemented these yet.

This test is necessarily quite slow, as we need to make sure we have had at least one aggregation period (10s). Waiting for 2 periods to avoid flake. Unfortunately the period is fixed at 10s by design (as this is a global setting per-metric in the backend) so can't be safely reduced for testing purposes.

There were already some ASM tests for metrics, so this extracts the logic already used there and shares it in the library interfaces

Motivation

We want to add system tests for telemetry features

Workflow

1. ⚠️⚠️ Create your PR as draft
2. Follow the style guidelines of this project (See how to easily lint the code)
3. Work on you PR until the CI passes (if something not related to your task is failing, you can ignore it)
4. Mark it as ready for review

Once your PR is reviewed, you can merge it! ❤️

Reviewer checklist

• Check what scenarios are modified. If needed, add the relevant label (run-parametric-scenario, run-profiling-scenario...). If this PR modifies any system-tests internal, then add the run-all-scenarios label (more info).
• CI is green
  • If not, failing jobs are not related to this change (and you are 100% sure about this statement)
• if any of build-some-image label is present
  1. is the image labl have been updated ?
  2. just before merging, locally build and push the image to hub.docker.com

[smola]

@andrewlock Lint was failing, I pushed the fix (run ./format.sh).