Enables Nextcloud data to be stored in S3

[mmeidlinger]

Nextcloud can be configured to store data in Amazon S3. Externalizing nextcloud data to S3 can be activated by configuring environment variables prior to running the installer. Authentication for this feature works on EC2 instances through EC2 instance roles.

By decoupling data storage from the actual mail server instance, increases portability, availability and resiliency of the data, while at the same time reducing cost and increasing scalability.