Storage Backend SFTP Environment

This is a glue module that connects two existing features: SFTP storage backends and server environment configuration. Once installed, the SFTP connection settings of a storage backend can be supplied by the server's environment configuration rather than being entered manually on the storage backend record.

The following SFTP settings become environment-managed: sftp_server, sftp_port, sftp_auth_method, sftp_login, sftp_password and sftp_ssh_private_key. This means an administrator can keep credentials and server addresses outside the database, which is useful for security and for deploying the same configuration across several databases.

When the module is installed, existing values already stored in the database for these fields are preserved so they are not lost. If the module is later uninstalled, the database columns that were removed by the environment mechanism are restored.

It adds no new menus or screens. It only extends the existing storage.backend model, so users keep working with storage backends as before; the difference is where the SFTP connection values come from.