make thumbnail, trashbin and version paths configurable

[butonic]

In large Installations storage cost can be improved by placing data on different storages, eg:

• thumbnails on SSDs for performance
• trash on cheaper HDDs
• versions on a ceph bucket
• data on a glusterfs (just as an example)

For scalability the data should be placed in prefixed user dirs in each case, eg:

• /mnt/oc_trash/al/ice/files_trashbin
• /mnt/oc_versions/bo/b/files_versions
• /mnt/oc_data/pe/ter/files
• /mnt/oc_thumbnails/to/m/thumbnails
• /mnt/oc_cache/to/m/cache

For cache we already have cache_path in the config.php. This FR just extends the functionality to other types of data and proposes to always prefix user dirs. It is not really needed to make that configurable. (although a userid prefix could be configured like 'userid_prefix' => '#/##' which would lead to data/p/et/er. Also keep in mind that the puth might come from the database in the future and no longer can or should be derived from the userid, as it may become a simple integer.)

[felixboehm]

Awesome!

[PVince81]

If we move the metadata to a separate folder like we did for avatars "data/avatars", this might become easier.

[PVince81]

Decouple home storages #29502 where we can go further and let the admin configure metadata storage as well.