plugin identity: Raise timeout:

5s timeout is too short, if the server is overloaded or connection is slow, it makes the
identity retrieval fail. 15s is more reasonable and matches timeout used for disco.

libervia/backend/plugins/plugin_misc_identity.py

@@ -807,7 +807,7 @@ class Identity:
                 )
             )
         deferred_list = defer.DeferredList(get_identity_list)
-        deferred_list.addTimeout(5, cast(IReactorCore, reactor))
+        deferred_list.addTimeout(15, cast(IReactorCore, reactor))
         identities_result = await deferred_list
         for idx, (success, identity) in enumerate(identities_result):
             entity_jid = entities[idx]