[feature] Linked folders and files (similar to hard / soft link functionality)

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Is your feature request related to a problem? Please describe.
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Problem description

I am administrating a NC instance with more than 1k users. When sharing data between different sub-communities, it has to be duplicated, which has two major disadvantages.

1 - Duplicates eat up storage space.
2 - Modified content needs to be versioned manually. This creates a large and unnecessary overhead.

This issue relates to past requests for deduplication and linking (e.g. #21560, #25562 and #19948).

Solution suggestion

A native way to make folders and files appear as linked, similar to federated folders. A reference could be the ownCloud implementation. The ownCloud instance at my workplace does indeed allow me to place shared folders and files into my own user space.

Alternatives considered

Currently, the only workarounds I have seen is the creation of links using URLs (URL files), or links in an overview document.

Additional context

Every file system supports linking in one or another other way, and every OS provides this feature to their users. Thus, every user will expect this feature from a cloud FS. If not present, it is perceived as a missing feature and a software shortcoming.

Start by reviewing the related issues #21560, #25562, and #19948, then compare the referenced ownCloud behavior. The issue names no implementation entry point, tests, or acceptance criteria; the work would need to define how linked folders and files avoid duplication while keeping shared modifications consistent.