[Response Ops][Connectors] New xpack.actions.webhook.ssl.pfx.enabled config (#222507)

## Summary

Closes https://github.com/elastic/kibana/issues/220416

## Release note
New `xpack.actions.webhook.ssl.pfx.enabled` Kibana setting to disable
Webhook connector PFX file support for SSL client authentication

---------

Co-authored-by: Nastasha Solomon <79124755+nastasha-solomon@users.noreply.github.com>

docs/reference/configuration-reference/alerting-settings.md

@@ -841,6 +841,12 @@ For more examples, go to [Preconfigured connectors](/reference/connectors-kibana
 
     Data type: `string`
 
+`xpack.actions.webhook.ssl.pfx.enabled`
+:   Disable PFX file support for SSL client authentication. When set to `false`, the application will not accept PFX certificate files and will require separate certificate and private key files instead. Only applies to the [Webhook connector](/reference/connectors-kibana/webhook-action-type.md).
+
+    Data type: `bool`
+    Default: `true`
+
 ## Alerting settings [alert-settings]
 
 `xpack.alerting.cancelAlertsOnRuleTimeout` ![logo cloud](https://doc-icons.s3.us-east-2.amazonaws.com/logo_cloud.svg "Supported on {{ech}}")

docs/settings-gen/source/kibana-alert-action-settings.yml

@@ -2303,6 +2303,27 @@ groups:
             self: all
          # example: |
 
+      - setting: xpack.actions.webhook.ssl.pfx.enabled
+        # id:
+        description: |
+          Disable PFX file support for SSL client authentication. When set to `false`, the application will not accept PFX certificate files and will require separate certificate and private key files instead. Only applies to the [Webhook connector](/reference/connectors-kibana/webhook-action-type.md).
+        # state: deprecated/hidden/tech-preview
+        # deprecation_details: ""
+        # note: ""
+        # tip: ""
+        # warning: ""
+        # important: ""
+        datatype: bool
+        default: true
+        # options:
+        #   - option:
+        #     description: ""
+        # type: static/dynamic
+        applies_to:
+          deployment:
+            self: all
+         # example: |
+
   - group: Alerting settings
     id: alert-settings
     # description: |