See #50898 for the implementation. Currently, an app developer needs to upload the env file via the command line upload tool. It would be better, to have it explicitly in the app provider portal.
This issue has been filed against an older version of UCS. With further development of our products affected components may have vastly changed while the corresponding use cases might have changed. Thus, this issue is now being closed. If there still is a need for this feature, please use "Clone this bug" or reopen this issue. In this case please provide information on how this issue would benefit you.