tests/redpanda: log the bootstrap cluster config

to complement the logging of node configurations. Note that
cluster_config.yaml records cluster config when nodes stop, whlie
this log dumps the initial bootstrap config.

tests/rptest/services/redpanda.py

@@ -3055,6 +3055,7 @@ def write_bootstrap_cluster_config(self):
             conf.update(dict(sasl_mechanisms=self._security.sasl_mechanisms))
 
         conf_yaml = yaml.dump(conf)
+        self.logger.debug(conf_yaml)
         for node in self.nodes:
             self.logger.info(
                 "Writing bootstrap cluster config file {}:{}".format(