[Extensions] Fixed duplicate extension unique id (#8228)

* Fixes duplicate extension unique id

Signed-off-by: Owais Kazi <owaiskazi19@gmail.com>

* Handled different extension unique id

Signed-off-by: Owais Kazi <owaiskazi19@gmail.com>

---------

Signed-off-by: Owais Kazi <owaiskazi19@gmail.com>
(cherry picked from commit f21d73e)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

server/src/main/java/org/opensearch/transport/TransportService.java

@@ -533,7 +533,10 @@ public ConnectionManager.ConnectionValidator connectionValidatorForExtensionConn
     ) {
         return (newConnection, actualProfile, listener) -> {
             // We don't validate cluster names to allow for CCS connections.
-            threadPool.getThreadContext().putHeader("extension_unique_id", extensionUniqueId);
+            String currentId = threadPool.getThreadContext().getHeader("extension_unique_id");
+            if (Strings.isNullOrEmpty(currentId) || !extensionUniqueId.equals(currentId)) {
+                threadPool.getThreadContext().putHeader("extension_unique_id", extensionUniqueId);
+            }
             handshake(newConnection, actualProfile.getHandshakeTimeout().millis(), cn -> true, ActionListener.map(listener, resp -> {
                 final DiscoveryNode remote = resp.discoveryNode;