Added one more entry to the query planner output when the plan is EOF to explain the type of EOF plan it is.

Description of Linked Ticket

The classic optimizer can create EOF plans for (at least?) two reasons: when the namespace doesn't exist and when expression simplification shows the query will not match any documents. I believe the second one is new as of SERVER-81863. It would be convenient to differentiate these cases in the explain output. For CQF, we will annotate the EOF stage with a description of why it was created. This ticket is to consider the same in classic.