Add support to custom user uploads dir

Is your feature request related to a problem? Please describe.
Hi Team, I notice that actually is not possible customize the path where temporary uploads ,<user_id>/uploads, are stored. This happen for example with Chunk file.

It's possible customize the temp path for PHP and so on, but ufter tmp path, chunks go into <user_id>/uploads and then, after assebling, will go to the standar data folder for user.

It will be cool, have a settings that will allow us to "link" <user_id>/uploads to specific path, where we can mount, for example, local storage, that in general is much faster than long term storage.

Describe the solution you'd like
Add a option to customize <user_id>/uploads or adding a symlink to it.

Describe alternatives you've considered
Actually there is no alternative apart disable chunking.

Additional context
I will send you a PR that will address this feature with usage of symlink and adding of new config parameter called uploadsdirectory.
More info in the PR.

Thanks

Start by locating the chunk-upload handling and the <user_id>/uploads path described in the issue, then trace how the proposed uploadsdirectory setting would interact with the standard data folder. Check existing storage-related tests and add coverage showing that the temporary upload location can be configured or linked without breaking assembly.