In theory it should be the cloud providers themselves maintaining the locally-runnable stand-ins for their services, but as it stands you basically either get it as a third party effort (MinIO for S3) or in cases where the service is just a hosted version of some existing OSS product (Postgres for RDS).
Either way, once the local version exists, then the job becomes maintaining all the infrastructure that lets you bring up the pieces, populate them with reasonable state and wire them into whatever the bits are that are being actively hacked-on.