Add cost estimate and CE for COUNT stage in explain

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Major - P3
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    • Affects Version/s: None
    • Component/s: None
    • Query Optimization
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      > db.adminCommand({setParameter:1, planRankerMode: "heuristicCE"})
> db.c.explain().find({a:1}).count()

"winningPlan" : {
  "isCached" : false,
  "stage" : "COUNT",
  "inputStage" : {
    "stage" : "COLLSCAN",
    "costEstimate" : 0.8720823999999999,
    "cardinalityEstimate" : 44.7548880012005,
    "numDocsEstimate" : 2003,
    "estimatesMetadata" : {
      "ceSource" : "Heuristics"
    },
    "filter" : {
      "a" : {
        "$eq" : 1
      }
    },
    "direction" : "forward"
  }
},

      The collscan is costed by the count stage is not.

            Assignee:
            Unassigned
            Reporter:
            Ben Shteinfeld
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              Created:
              Updated: