Choose the container to upload files to

For the moment, only one URI container is passed in the data provider config.

This could be interesting if we could define, for example in the Input components, in which container we want to post the files.

Start by tracing how the data provider configuration supplies the single URI container and how Input components submit files. Define how an Input component selects its target container, then verify that files are posted to the selected container while existing behavior remains unchanged.

Written by the indexing model from the issue text.