Create concatArrays accumulator

Author: paulinevos

generator/config/accumulator/concatArrays.yaml

@@ -0,0 +1,30 @@
+# $schema: ../schema.json
+name: $concatArrays
+link: 'https://www.mongodb.com/docs/manual/reference/operator/aggregation/concatArrays/'
+type:
+  - accumulator
+  - window
+  - resolvesToArray
+encode: single
+description: |
+  Concatenates arrays to return the concatenated array.
+arguments:
+  -
+    name: array
+    type:
+      - resolvesToArray # of arrays
+    variadic: array
+    description: |
+      An array of expressions that resolve to an array. 
+      If any argument resolves to a value of null or refers to a field that is missing, `$concatArrays` returns `null`.
+tests:
+  -
+    name: 'Warehouse collection'
+    link: 'https://www.mongodb.com/docs/manual/reference/operator/aggregation/concatArrays/#example'
+    pipeline:
+      -
+        $project:
+          items:
+            $concatArrays:
+              - '$instock'
+              - '$ordered'