Expose Logs of OpenSearch
Make the logs of the data node's OpenSearch available in the UI. This should also include the logs for remote reindexing in the migration wizard.
Currently the datanode provides https://localhost:8999/logs/stdout and https://localhost:8999/logs/stderr by default. See https://github.com/Graylog2/graylog2-server/blob/master/data-node/src/main/java/org/graylog/datanode/rest/LogsController.java. We just need a proxy or access to the datanode REST from the graylog server to display these.
Both stdout and stderr now available through the datanode proxy:
http://localhost:9000/api/datanodes/rest/logs/stdout http://localhost:9000/api/datanodes/rest/logs/stderr