Rename AWS S3 Terraform outputs

[jochenehret]

The new names harmonize better with the cf-deployment ops files:

• https://github.com/cloudfoundry/cf-deployment/blob/main/operations/use-external-blobstore.yml
• https://github.com/cloudfoundry/cf-deployment/blob/main/operations/use-s3-blobstore.yml

Note that this is a breaking change and should be mentioned in the release notes.