pipeline: outputs: es: HTTP_API_Key option documentation copied from fluent#1727.

Signed-off-by: Marat Abrarov <[email protected]>

Author: mabrarov

pipeline/outputs/elasticsearch.md

@@ -33,6 +33,7 @@ configuration.
 | `Cloud_Auth` | Specify the credentials to use to connect to Elastic's Elasticsearch Service running on Elastic Cloud. | _none_ | Yes |
 | `HTTP_User` | Optional username credential for Elastic X-Pack access. | _none_ | Yes |
 | `HTTP_Passwd` | Password for user defined in `HTTP_User`. | _none_ | Yes |
+| `HTTP_API_Key` | API key for authenticating with Elasticsearch. Must be `base64` encoded. If `HTTP_User` or `Cloud_Auth` are defined, this parameter is ignored. | _none_ | Yes |
 | `Index` | Index name. | `fluent-bit` | Yes |
 | `Type` | Type name. | `_doc` | Yes |
 | `Logstash_Format` | Enable Logstash format compatibility. This option takes a Boolean value: `True/False`, `On/Off`. | `Off` | Yes |