New feature: support for fifo topics

[rhiroyuki]

Introducing SNS FIFO Topics
Today, we are adding similar capabilities for pub/sub messaging with the introduction of SNS FIFO topics, providing strict message ordering and deduplicated message delivery to one or more subscribers.

https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/SNS/Client.html#create_topic-instance_method
https://aws.amazon.com/blogs/aws/introducing-amazon-sns-fifo-first-in-first-out-pub-sub-messaging/