How to draw static line across a graph?

I’m creating a real time graph to plot latency with plotly.js and it works well.

I want to draw a redline horizontally to denote the SLA for latency. The idea is to provide a visual cue if latency is breaching SLA.

Is there a method to do this?

Thank you! might be a good place to start.

Is there a way of getting lines without using shapes?