Instead of providing SSL certificates via helm values.yaml it is more secure to mount existing secrets and configure the certificate path of mounted files in custom rabbitmq.conf options.
Adapt the config. and remove cert. inline options
Set initial default user and password value to NIL and allow optional env. variables (RABBITMQ_DEFAULT_USER, RABBITMQ_DEFAULT_PASS). If nothing is set RabbitMQ will use "guest"/"guest".