Delegate Opal file storage

[ymarcon]

Currently the Opal's file storage is the host's file system. It could be interesting to delegate file storage to a file store application such as, MongoFS or S3 compatible systems (such as MinIO). This can be an extra feature, using a plugin (SPI to be defined) that declares a file system and a mount point (/projects could be located at a different place than /home for instance).