Store completion and/or metric errors

[levon003]

Currently, Config exposes boolean flags for terminating if errors occur while computing completions or metrics.

• Should we allow FlexEval to proceed after errors during completion?
  • If yes, how should we record that error state in the database?
• Should we allow FlexEval to proceed after errors during metric computation?
  • If yes, how should we record that error state in the database?