Support mode, db, and uniqueKey for aggregation $out stage

SCALA-473

Author: jyemin

driver/src/main/scala/org/mongodb/scala/model/Aggregates.scala

@@ -339,11 +339,21 @@ object Aggregates {
   def unwind(fieldName: String, unwindOptions: UnwindOptions): Bson = JAggregates.unwind(fieldName, unwindOptions)
 
   /**
-   * Creates a `\$out` pipeline stage for the specified filter
+   * Creates a `\$out` pipeline stage that writes to the collection with the specified name
    *
    * @param collectionName the collection name
    * @return the `\$out` pipeline stage
    * @see [[http://docs.mongodb.org/manual/reference/operator/aggregation/out/  \$out]]
    */
   def out(collectionName: String): Bson = JAggregates.out(collectionName)
+
+  /**
+   * Creates a `\$out` pipeline stage that writes to the collection with the specified name, using the specified options
+   *
+   * @param collectionName the collection name
+   * @param options the options
+   * @return the `\$out` pipeline stage
+   * @see [[http://docs.mongodb.org/manual/reference/operator/aggregation/out/  \$out]]
+   */
+  def out(collectionName: String, options: AggregateOutStageOptions): Bson = JAggregates.out(collectionName, options)
 }

driver/src/main/scala/org/mongodb/scala/model/package.scala

@@ -79,6 +79,22 @@ package object model {
     def apply(): BucketOptions = new com.mongodb.client.model.BucketOptions()
   }
 
+  /**
+   * The options for a \$out aggregation pipeline stage
+   *
+   * @since 2.6
+   */
+  type AggregateOutStageOptions = com.mongodb.client.model.AggregateOutStageOptions
+
+  /**
+   * The options for a \$out aggregation pipeline stage
+   *
+   * @since 2.6
+   */
+  object AggregateOutStageOptions {
+    def apply(): AggregateOutStageOptions = new com.mongodb.client.model.AggregateOutStageOptions()
+  }
+
   /**
    * Granularity values for automatic bucketing.
    *

driver/src/test/scala/org/mongodb/scala/model/AggregatesSpec.scala

@@ -200,6 +200,9 @@ class AggregatesSpec extends FlatSpec with Matchers {
 
   it should "render $out" in {
     toBson(out("authors")) should equal(Document("""{ $out : "authors" }"""))
+    toBson(out("authors", AggregateOutStageOptions().databaseName("foo"))) should equal(
+      Document("""{ $out : {mode: "replaceCollection", to: "authors", db: "foo" } }""")
+    )
   }
 
   it should "render $group" in {