Bugfix: Prevent all inserts into experiment_error table, log instead

[danoswaltCL]

In issue #1040 I commented out errorService.create() usage for the ErrorHandler middleware due to concerns about size and relevancy of the experiment_error table in an effort to cut off new inserts to this table while we determined what we wanted to do with it.

This left 2 places though where inserts can still happen, and these are still getting into the table and causing a problem because the table is still growing too fast.

The suggested fix here will finish that job and instead log the events instead of inserting them in the db.

This is a release bugfix because it will also make sure to prevent the profusion of "417" SERVER_ERROR.EXPERIMENT_USER_GROUP_NOT_DEFINED errors in prod when running group experiments, which are causing this table to grow pointlessly.