Add support for $slice in projection stage of aggregation [DATAMONGO-1457]

[spring-projects-issues]

Oliver Eberle opened DATAMONGO-1457 and commented

As of MongoDB 3.2 $slice can be used to limit results from group $push operations.

{ $group: { _id : "$path", count: { $sum : 1 }, data : { $push : { _id:"$_id", name: "$name" }   } }},
{ $project : { data : { $slice : ["$data",0,10]}}},

Limit the data array to 10.

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Affects: 1.9.1 (Hopper SR1)

Referenced from: pull request #372