Add a section to AutoML user guide about extending an AutoML run

Description

We should add a section about re-running AutoML with a new seed on the same project. Note: must set `keep_cross_validation_predictions = TRUE` if we want to get Stacked Ensembles on the second run that include all the models (including the new ones).

Assignee

Erin LeDell

Reporter

Erin LeDell