Ensure auto minor version upgrade is enabled for AWS MQ Brokers

Message brokers if not configured to auto upgrade to the latest minor version could increase the likelihood of getting exploited.

In AWS Console -

1. Sign in to the AWS Console and go to the MQ dashboard.
2. In the navigation panel, Select Brokers.
3. In the Broker details tab select Edit.
4. Under Maintenance, Enable automatic minor version upgrades.

In Terraform -

1. In the aws_mq_broker resource, set the auto_minor_version_upgrade field to true.

References:
https://docs.aws.amazon.com/amazon-mq/latest/developer-guide/upgrading-brokers.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/mq_broker#auto_minor_version_upgrade