Sets the timeout used for adding a downstream connection in LogScale Multi-Cluster Search. When submitting a new query in Multi-Cluster Search, a connection request to the downstream clusters are submitted. If the time between the first submission and the latest submission is greater than the submission timeout (1 hour by default), then the connection will be aborted and an empty result will be merged as a placeholder for that connection. Furthermore, a warning named FederatedSubmissionTimeout is added to the query. The timeout can be changed using this environment variable.