[Exploratory View] Make Synthetics Series "Monitor" and "Step" Options Single select

[drewpost]

To avoid creating meaningless datasets which would result from creating an average of a metric across multiple monitors and to prevent UX confusion with commonly named steps across multiple monitors showing up in the steps menu, we should implement the following:

In a synthetics series:

• Monitor field is single select

• The step name field related to the monitor is single select

• If no monitor is selected BUT there's a value in the URL field - that value will show the requested metric across all matching instances of that URL across every monitor and step

• If a monitor and or step is selected then the URL filter will show results only for matching URLs within the selected monitor and or step.