[ML] Detectors using scripted fields with model plot enabled should be viewable in the Single Metric Viewer

[peteharverson]

Metric data from detectors which use a scripted field cannot currently be viewed in the Anomaly Explorer or the Single Metric Viewer (see #18464) due to the difficulty of 'reverse engineering' the scripted field query in order to draw the chart. However if model plot has been enabled for the job, the detector should be viewable in the Single Metric Viewer since it then uses the model plot data to draw the chart and there is no need to 'reverse engineer' the scripted field configuration.

[elasticmachine]

Pinging @elastic/ml-ui