PHPLIB-1695 Add $createObjectId operator to the agg builder (#1738)

Author: GromNaN

generator/config/expression/createObjectId.yaml

@@ -0,0 +1,17 @@
+# $schema: ../schema.json
+name: $createObjectId
+link: 'https://www.mongodb.com/docs/manual/reference/operator/aggregation/createObjectId/'
+type:
+  - resolvesToObjectId
+encode: object
+description: |
+  Returns a random object ID
+tests:
+  -
+    name: 'Example'
+    link: 'https://www.mongodb.com/docs/manual/reference/operator/aggregation/createObjectId/#example'
+    pipeline:
+      -
+        $project:
+          objectId:
+            $createObjectId: {}

src/Builder/Expression/CreateObjectIdOperator.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MongoDB\Tests\Builder\Expression;
+
+use MongoDB\Builder\Expression;
+use MongoDB\Builder\Pipeline;
+use MongoDB\Builder\Stage;
+use MongoDB\Tests\Builder\PipelineTestCase;
+
+/**
+ * Test $createObjectId expression
+ */
+class CreateObjectIdOperatorTest extends PipelineTestCase
+{
+    public function testExample(): void
+    {
+        $pipeline = new Pipeline(
+            Stage::project(
+                objectId: Expression::createObjectId(),
+            ),
+        );
+
+        $this->assertSamePipeline(Pipelines::CreateObjectIdExample, $pipeline);
+    }
+}