ingest: raise visibility of ingest plugin documentation (#35048)

* move the set security user processor to the main documentation
* link to plugin processors

part of #33188

docs/reference/ingest/ingest-node.asciidoc

@@ -764,6 +764,12 @@ A node will not start if either of these plugins are not available.
 The <<ingest-stats,node stats API>> can be used to fetch ingest usage statistics, globally and on a per
 pipeline basis. Useful to find out which pipelines are used the most or spent the most time on preprocessing.
 
+[float]
+=== Ingest Processor Plugins
+
+Additional ingest processors can be implemented and installed as Elasticsearch {plugins}/intro.html[plugins].
+See {plugins}/ingest.html[Ingest plugins] for information about the available ingest plugins.
+
 [[append-processor]]
 === Append Processor
 Appends one or more values to an existing array if the field already exists and it is an array.
@@ -2440,6 +2446,43 @@ include::ingest-node-common-processor.asciidoc[]
 --------------------------------------------------
 // NOTCONSOLE
 
+
+[[ingest-node-set-security-user-processor]]
+=== Set Security User Processor
+Sets user-related details (such as `username`,  `roles`, `email`, `full_name`
+and `metadata` ) from the current
+authenticated user to the current document by pre-processing the ingest.
+
+IMPORTANT: Requires an authenticated user for the index request.
+
+[[set-security-user-options]]
+.Set Security User Options
+[options="header"]
+|======
+| Name          | Required  | Default                                                   | Description
+| `field`       | yes       | -                                                         | The field to store the user information into.
+| `properties`  | no        | [`username`, `roles`, `email`, `full_name`, `metadata`]   | Controls what user related properties are added to the `field`.
+include::ingest-node-common-processor.asciidoc[]
+|======
+
+The following example adds all user details for the current authenticated user
+to the `user` field for all documents that are processed by this pipeline:
+
+[source,js]
+--------------------------------------------------
+{
+  "processors" : [
+    {
+      "set_security_user": {
+        "field": "user"
+      }
+    }
+  ]
+}
+--------------------------------------------------
+// NOTCONSOLE
+
+
 [[split-processor]]
 === Split Processor
 Splits a field into an array using a separator character. Only works on string fields.

x-pack/docs/en/security/authorization/set-security-user.asciidoc

@@ -9,53 +9,18 @@ To guarantee that a user reads only their own documents, it makes sense to set u
 document level security. In this scenario, each document must have the username
 or role name associated with it, so that this information can be used by the
 role query for document level security. This is a situation where the
-`set_security_user` ingest processor can help.
+{ref}/ingest-node-set-security-user-processor.html[Set Security User Processor] ingest processor can help.
 
 NOTE: Document level security doesn't apply to write APIs. You must use unique
 ids for each user that uses the same index, otherwise they might overwrite other
 users' documents. The ingest processor just adds properties for the current
 authenticated user to the documents that are being indexed.
 
-The `set_security_user` processor attaches user-related details (such as
+The {ref}/ingest-node-set-security-user-processor.html[set security user processor] attaches user-related details (such as
 `username`,  `roles`, `email`, `full_name` and `metadata` ) from the current
 authenticated user to the current document by pre-processing the ingest. When
 you index data with an ingest pipeline, user details are automatically attached
-to the document. For example:
+to the document.
 
-[source,js]
---------------------------------------------------
-PUT shared-logs/log/1?pipeline=my_pipeline_id
-{
-  ...
-}
---------------------------------------------------
-// NOTCONSOLE
+For more information see {ref}/ingest.html[Ingest node] and {ref}/ingest-node-set-security-user-processor.html[Set security user processor].
 
-For more information about setting up a pipeline and other processors, see 
-{ref}/ingest.html[ingest node].
-
-[[set-security-user-options]]
-.Set Security User Options
-[options="header"]
-|======
-| Name          | Required  | Default                                                   | Description
-| `field`       | yes       | -                                                         | The field to store the user information into.
-| `properties`  | no        | [`username`, `roles`, `email`, `full_name`, `metadata`]   | Controls what user related properties are added to the `field`.
-|======
-
-The following example adds all user details for the current authenticated user
-to the `user` field for all documents that are processed by this pipeline:
-
-[source,js]
---------------------------------------------------
-{
-  "processors" : [
-    {
-      "set_security_user": {
-        "field": "user"
-      }
-    }
-  ]
-}
---------------------------------------------------
-// NOTCONSOLE