Support new 4.20 style file storage location configuration

[poikilotherm]

Since 4.20, a few things changed when configuring a data storage location. Instead of a single place for everything, you may configure multiple storages and choose between those per Dataverse.

• Support for defining the storage locations is already present via env vars from the ConfigMap
• By default, dataverse.files.storage-driver-id points to file. We will create and use one with id local to be more human readable.
• We should provide an opt-out default file storage based on /data.
  • This is mimicking the current behaviour, but enables flexibility when no local storage should be available (production instances) but deserved for testing, docker-compose usage etc.
  • When dataverse.files.storage-driver-id=local, we configure this as our local storage. When someone configures some other storage as default (like an S3 storage), it will most likely either have a different id or at least will overwrite the necessary configuration bits.
• By default, dataverse.files.directory=/data will continue to drop any temp data (uploads, ...) at /data/temp. (The temp dir is created by Dataverse).

The docs need to reflect the changes:

• Update example ConfigMap (S3 storage options!)
• Fix strange inclusion line numbers of configuration help page.
• Add a link to the storage explanaition in upstream docs, as those aren't well described in the JVM options overview.
• On storage page, describe the /data/temp thing and it's corresponding JVM option.
• Also on storage page, describe options how to configure multiple storages plus link to and from configuration page. (So basically this sounds like a new section about remote storage and an addition about local storage)