Provide REST API to return long-running tasks for all nodes at once, instead of only one node.

When querying for long-running tasks using the /rest/api/longtask REST API on a Confluence DC instance, the response currently only contains the tasks tracked by the specific node that handled the query. This leads to inconsistent results, as the same REST request can return different responses depending on which node processes the request.

To improve consistency and provide a clear view of all long-running tasks across the entire cluster, the there should be a way to use the REST API to return all long-running tasks from all nodes in the Confluence Data Center instance.