Support adding prefix/subfolder under an S3 bucket for Redshift

Is your feature request related to a problem? Please describe. Ccube does not support adding prefix/subfolder under an S3 bucket in .env file. If you try to hard-code path after the bucket name it will have errors like: InvalidBucketName: Bucket name shouldn't contain '/', received (your wrong path here)

Describe the solution you'd like Maybe to have CUBEJS_DB_EXPORT_BUCKET changed to CUBEJS_DB_EXPORT_PATH

Describe alternatives you've considered