Add foreach processor documentation (#5981)

* Add foreach processor documentation

Signed-off-by: Melissa Vagi <[email protected]>

* Add pipeline example requests and responses

Signed-off-by: Melissa Vagi <[email protected]>

* Add pipeline examples

Signed-off-by: Melissa Vagi <[email protected]>

* Address tech review comments

Signed-off-by: Melissa Vagi <[email protected]>

* Update _ingest-pipelines/processors/foreach.md

Co-authored-by: Nathan Bower <[email protected]>
Signed-off-by: Melissa Vagi <[email protected]>

* Update _ingest-pipelines/processors/foreach.md

Co-authored-by: Nathan Bower <[email protected]>
Signed-off-by: Melissa Vagi <[email protected]>

* Address editorial review comments

Signed-off-by: Melissa Vagi <[email protected]>

---------

Signed-off-by: Melissa Vagi <[email protected]>
Co-authored-by: Nathan Bower <[email protected]>
(cherry picked from commit fe979d5)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

_ingest-pipelines/processors/foreach.md

@@ -0,0 +1,209 @@
+---
+layout: default
+title: `foreach`
+parent: Ingest processors
+nav_order: 110
+---
+
+# `foreach` processor
+
+The `foreach` processor is used to iterate over a list of values in an input document and apply a transformation to each value. This can be useful for tasks like processing all the elements in an array consistently, such as converting all elements in a string to lowercase or uppercase.
+
+The following is the syntax for the `foreach` processor:
+
+```json
+{
+  "foreach": {
+    "field": "<field_name>",
+    "processor": {
+      "<processor_type>": {
+        "<processor_config>": "<processor_value>"
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Configuration parameters
+
+The following table lists the required and optional parameters for the `foreach` processor.
+
+Parameter | Required/Optional | Description |
+|-----------|-----------|-----------|
+`field` | Required | The array field to iterate over.
+`processor` | Required | The processor to execute against each field.
+`ignore_missing` | Optional | If `true` and the specified field does not exist or is null, then the processor will quietly exit without modifying the document.
+`description` | Optional | A brief description of the processor.
+`if` | Optional | A condition for running the processor.
+`ignore_failure` | Optional | Specifies whether the processor continues execution even if it encounters an error. If set to `true`, then failures are ignored. Default is `false`.
+`on_failure` | Optional | A list of processors to run if the processor fails.
+`tag` | Optional | An identifier tag for the processor. Useful for debugging in order to distinguish between processors of the same type.
+
+## Using the processor
+
+Follow these steps to use the processor in a pipeline.
+
+### Step 1: Create a pipeline
+
+The following query creates a pipeline named `test-foreach` that uses the `foreach` processor to iterate over each element in the `protocols` field: 
+
+```json
+PUT _ingest/pipeline/test-foreach  
+{  
+  "description": "Lowercase all the elements in an array",  
+  "processors": [  
+    {  
+      "foreach": {  
+        "field": "protocols",  
+        "processor": {  
+          "lowercase": {  
+            "field": "_ingest._value"  
+          }  
+        }  
+      }  
+```
+{% include copy-curl.html %}
+
+### Step 2 (Optional): Test the pipeline
+
+It is recommended that you test your pipeline before you ingest documents.
+{: .tip}
+
+To test the pipeline, run the following query:
+
+```json
+POST _ingest/pipeline/test-foreach/_simulate  
+{  
+  "docs": [  
+    {  
+      "_index": "testindex1",  
+      "_id": "1",  
+      "_source": {  
+        "protocols": ["HTTP","HTTPS","TCP","UDP"]  
+      }  
+    }  
+  ]  
+} 
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The following example response confirms that the pipeline is working as expected, showing that the four elements have been lowercased:
+
+```json
+{  
+  "docs": [  
+    {  
+      "doc": {  
+        "_index": "testindex1",  
+        "_id": "1",  
+        "_source": {  
+          "protocols": [  
+            "http",  
+            "https",  
+            "tcp",  
+            "udp"  
+          ]  
+        },  
+        "_ingest": {  
+          "_value": null,  
+          "timestamp": "2024-05-23T02:44:10.8201Z"  
+        }  
+      }  
+    }  
+  ]  
+}  
+
+```
+{% include copy-curl.html %}
+
+### Step 3: Ingest a document 
+
+The following query ingests a document into an index named `testindex1`:
+
+```json
+POST testindex1/_doc/1?pipeline=test-foreach  
+{  
+  "protocols": ["HTTP","HTTPS","TCP","UDP"]  
+}  
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The request indexes the document into the index `testindex1` and applies the pipeline before indexing:
+
+```json
+{  
+  "_index": "testindex1",  
+  "_id": "1",  
+  "_version": 6,  
+  "result": "created",  
+  "_shards": {  
+    "total": 2,  
+    "successful": 1,  
+    "failed": 0  
+  },  
+  "_seq_no": 5,  
+  "_primary_term": 67  
+}  
+```
+{% include copy-curl.html %}
+
+### Step 4 (Optional): Retrieve the document
+
+To retrieve the document, run the following query:
+
+```json
+GET testindex1/_doc/1
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The response shows the document with the extracted JSON data from the `users` field:
+
+```json
+{  
+  "_index": "testindex1",  
+  "_id": "1",  
+  "_version": 6,  
+  "_seq_no": 5,  
+  "_primary_term": 67,  
+  "found": true,  
+  "_source": {  
+    "protocols": [  
+      "http",  
+      "https",  
+      "tcp",  
+      "udp"  
+    ]  
+  }  
+}  
+
+{  
+  "docs": [  
+    {  
+      "doc": {  
+        "_index": "testindex1",  
+        "_id": "1",  
+        "_source": {  
+          "protocols": [  
+            "http",  
+            "https",  
+            "tcp",  
+            "udp"  
+          ]  
+        },  
+        "_ingest": {  
+          "_value": null,  
+          "timestamp": "2024-05-23T02:44:10.8201Z"  
+        }  
+      }  
+    }  
+  ]  
+}  
+```
+{% include copy-curl.html %}