Ensure that all components have a requestRate metric

Before this change, the metrics catalog had three optional metrics for each componet: apdex, requestRate and error rate.

However, it turns out that if a metric does not have a request rate, other alerts may not fire:

• Error ratio alerts rely on error rate and request rate
• Apdex alerts use a minimum RPS threshold to prevent noise

Therefore, it's necessary that all components have a mandatory requestRate metric.

This ensures that by adding validation to the metrics catalog.

This should also make it easier for new developers to add metrics as they can get feedback on whether they're doing the right thing.

Additional request rate metrics

The gitalyruby and rails_sql components did not have requestRate metrics and where therefore not being alerted on.

In order to pass the new validation that has been added, this change includes requestRate metrics for both of these components.