Make TelemetrySubmissionPeriodical leader-only (#24145)

* Make TelemetrySubmissionPeriodical leader-only

* Add changelog

---------

Co-authored-by: Florian Petersen <188503754+fpetersen-gl@users.noreply.github.com>

changelog/unreleased/pr-24145.toml

@@ -0,0 +1,4 @@
+type = "c"
+message = "Backend telemetry is now sent only by the leader node."
+
+pulls = ["24145"]

graylog2-server/src/main/java/org/graylog2/telemetry/scheduler/TelemetrySubmissionPeriodical.java

@@ -101,4 +101,9 @@ public class TelemetrySubmissionPeriodical extends Periodical {
     protected Logger getLogger() {
         return LOG;
     }
+
+    @Override
+    public boolean leaderOnly() {
+        return true;
+    }
 }