Upgrade to Spring Boot 4.1.0-RC1

Bumps Spring Boot, Framework, Security, AMQP, Kafka and LDAP to the
4.1.0-RC1-aligned versions, drops the Artemis 2.43.0 workaround now
that Boot 4.1 ships Artemis 2.53.0, and adapts to two source-level
breaking changes:

- Spring Kafka 4.1 added KafkaListenerEndpoint#getAckMode() as a
  required method; SimpleKafkaListenerEndpoint now implements it.
- Spring AMQP 4.1 deprecated org.springframework.amqp.rabbit.listener
  .MessageListenerContainer in favor of the core variant, which is
  what RabbitListenerEndpointRegistry now returns.