Allow transaction.duration: to be used as an event filter for Metric alerts

### Problem Statement

When creating a performance alert using Percent Change as the Set Threshold, it's possible that the previous time period has a duration of 0 if it is a transaction that is not run at all times. This causes the percent change alerts to not be very useful.

**Example** -

### Solution Brainstorm

Allowing `transaction.duration:` to be used as a filter in the Filter Events section of the alert can prevent this and ensure only transactions with durations populate the charts and alerts.