Introduce new validation step for verifying configured Azure Monitor metrics

[tomkerkhove]

Introduce new validation step for verifying configured Azure Monitor metrics at startup.

For every single configured metric it should:

• [ ] Verify that it has access to query it
• [ ] Verify that the configured metric name exists
• [ ] Verify that the configured aggregation interval exactly matches with what is supported
• [ ] Verify that the configured dimension is supported if configured

Every failure of the above should have a clear description that it failed and why it failed. No exceptions should be bubbled up as it will only be noise in the telemetry.

Next to unit tests we'll need to add integration tests for these scenarios which should also be added to the CI, although that will be done via #463

[tomkerkhove]

This is becoming more and more important, prioritizing.