Add missing "create" privilege to documentation

Users following our documentation are frustrated to discover that they get 403 errors from Logstash, even when following the instructions to the letter.  The problem is that the `create` privilege is missing. With this in place, it works as designed.

These changes may need to be back ported to previous branches, too.

Fixes #11013

Author: untergeek

docs/static/security/logstash.asciidoc

@@ -37,7 +37,7 @@ To set up authentication credentials for Logstash:
 
 . Use the the **Management > Roles** UI in {kib} or the `role` API to create a
 `logstash_writer` role. For *cluster* privileges, add `manage_index_templates` and `monitor`. 
-For *indices* privileges, add `write`, `delete`, and `create_index`.
+For *indices* privileges, add `write`, `create`, `delete`, and `create_index`.
 +
 If you plan to use {ref}/getting-started-index-lifecycle-management.html[index lifecycle
 management], also add `manage_ilm` for cluster and `manage` and `manage_ilm` for indices.
@@ -50,7 +50,7 @@ POST _xpack/security/role/logstash_writer
   "indices": [
     {
       "names": [ "logstash-*" ], <2>
-      "privileges": ["write","delete","create_index","manage","manage_ilm"]  <3>
+      "privileges": ["write","create","delete","create_index","manage","manage_ilm"]  <3>
     }
   ]
 }