cdc: support aws sns as a cdc native sink

AWS's Simple Notification Service (SNS) is a managed pub/sub messaging service that fans messages published to an SNS topic to multiple subscribers. There is a [workaround](https://dev.to/cockroachlabs/from-cockroachdb-to-aws-sns-via-cdc-and-aws-api-gateway-bna) to hook CRDB changefeeds to SNS, but there's a growing need for native, more performant and easy-to-use support. A solution to this issue would be to add a new sink supported by CDC.

Jira issue: CRDB-62021

Epic CRDB-42701