Handle "performance-infeasible" blueprints #335
Description
We have not yet implemented "performance infeasibility" in the blueprint planner (e.g., the candidate blueprint is predicted to have a query latency that exceeds a ceiling). Right now, blueprints are ordered based on a custom comparator. Blueprints with performance scores above the ceiling are ordered based on performance.
It would be useful to warn the user when all the candidate blueprints are "infeasible" (e.g., so they can set a better set of constraints).