[DOCS] Add Fleet setting for integration rollback TTL (#242270)

## Summary

This PR adds a description for the `xpack.fleet.integrationRollbackTTL`
setting to:

- Fleet settings in Kibana doc
- Elastic Cloud Kibana settings doc

Related to elastic/docs-content#3850
Contributes to closing
elastic/ingest-docs#1868

Author: vishaangelova

docs/reference/cloud/elastic-cloud-kibana-settings.md

@@ -82,6 +82,9 @@ stack: ga 9.3
 `xpack.actions.email.maximum_body_length`
 :    The maximum length of an email body in bytes.  Values longer than this length will be truncated.  The default is 25MB, the maximum is 25MB.
 
+`xpack.fleet.integrationRollbackTTL`
+:   Configure the time-to-live (TTL) for integration rollback availability. This setting controls how long the rollback option remains available after an integration is upgraded. The value must be specified in a duration format (for example, `7d`, `14d`, `168h`, or `1w`). Defaults to `7d` (7 days). For more information, refer to [Roll back an integration](docs-content://reference/fleet/roll-back-integration.md).
+
 ### Version 9.2+ [ec_version_9_2]
 ```{applies_to}
 stack: ga 9.2

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

@@ -352,3 +352,6 @@ These settings are not supported to pre-configure the Endpoint and Cloud Securit
 
 `xpack.fleet.autoUpgrades.retryDelays` ![logo cloud](https://doc-icons.s3.us-east-2.amazonaws.com/logo_cloud.svg "Supported on {{ech}}") {applies_to}`stack: ga 9.1`
 :   Configure the retry delays of the automatic upgrade task for {{fleet}}-managed {{agents}}. The array's length indicates the maximum number of retries. Defaults to `['30m', '1h', '2h', '4h', '8h', '16h', '24h']`.
+
+`xpack.fleet.integrationRollbackTTL` ![logo cloud](https://doc-icons.s3.us-east-2.amazonaws.com/logo_cloud.svg "Supported on {{ech}}") {applies_to}`stack: ga 9.3`
+:   Configure the time-to-live (TTL) for integration rollback availability. This setting controls how long the rollback option remains available after an integration is upgraded. The value must be specified in a duration format (for example, `7d`, `14d`, `168h`, or `1w`). Defaults to `7d` (7 days). For more information, refer to [Roll back an integration](docs-content://reference/fleet/roll-back-integration.md).