Add ingest-attachment-with-arrays section to ingest attachments doc

Added a new section detailing how to use the attachment processor
within an array.

This reverts commit #22296 and instead links to the foreach processor.

docs/plugins/ingest-attachment.asciidoc

@@ -106,4 +106,54 @@ NOTE: Extracting contents from binary data is a resource intensive operation and
       consumes a lot of resources. It is highly recommended to run pipelines
       using this processor in a dedicated ingest node.
       
-NOTE: To process an array of attachments the {ref}/foreach-processor.html[foreach processor] is required.
+[[ingest-attachment-with-arrays]]
+==== Using the Attachment Processor with arrays
+
+To use the attachment processor within an array of attachments the
+{ref}/foreach-processor.html[foreach processor] is required. This
+enables the attachment processor to be run on the individual elements
+of the array.
+
+For example, given the following source:
+
+[source,js]
+--------------------------------------------------
+{
+  "attachments" : [
+    {
+      "filename" : "ipsum.txt",
+      "data" : "dGhpcyBpcwpqdXN0IHNvbWUgdGV4dAo="
+    },
+    {
+      "filename" : "test.txt",
+      "data" : "VGhpcyBpcyBhIHRlc3QK"
+    }
+  ]
+}
+--------------------------------------------------
+
+In this case, we want to process the data field in each element
+of the attachments field and insert
+the properties into the document so the following `foreach`
+processor is used:
+
+[source,js]
+--------------------------------------------------
+{
+  "foreach": {
+    "field": "attachments",
+    "processor": {
+      "attachment": {
+        "target_field": "_ingest._value.attachment",
+        "field": "_ingest._value.data"
+      }
+    }
+  }
+}
+--------------------------------------------------
+Note that the `target_field` needs to be set, otherwise the
+default value is used which is a top level field `attachment`. The
+properties on this top level field will contain the value of the
+first attachment only. However, by specifying the
+`target_field` on to a value on `_ingest._value` it will correctly
+associate the properties with the correct attachment.

docs/reference/ingest/ingest-node.asciidoc

@@ -1166,6 +1166,10 @@ In this example, if the `remove` processor does fail, then
 the array elements that have been processed thus far will
 be updated.
 
+Another advanced example can be found in {plugins}/using-ingest-attachment.html[attachment processor documentation].
+
+
+
 [[grok-processor]]
 === Grok Processor