Support RO Ingestion Folder from golden source

[Webreaper]

What type of request is this?

New feature idea

Clear and concise description of the feature you are proposing

It would be fantastic if the ingestion folder could be set to be an RO docker-mount to my existing documents folder, and Papra would just scan that folder, indexing documents in place without having to copy/ingest them into Papra's own internal storage. Papra would monitor the docs and changes, and re-index any as/when they change.

Additional context

You mention in the docs the 'no mutation principle' - the best way to implement this is just to point Papra at an RO folder of my docs, and it just indexes them and makes them searchable.

Validations

• Check the feature is not already implemented in the project.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Check that the feature is technically feasible and aligns with the project's goals.