Add support for $filter to aggregation [DATAMONGO-1491]

[spring-projects-issues]

Christoph Strobl opened DATAMONGO-1491 and commented

see: https://docs.mongodb.com/manual/reference/operator/aggregation/filter/

{ $filter: { input: <array>, as: <string>, cond: <expression> } }

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Reference URL: http://stackoverflow.com/questions/39459898/

Referenced from: pull request #412

Backported to: 1.10 RC1 (Ingalls)