Refactor the getDocument method in KsDocumentController to return a single KSDocument object instead of a list. This improves the efficiency and readability of the code. The method now uses the findById method of ksDocumentRepository to retrieve the document with the specified id.
The code changes include adding a new endpoint `/files` to the `KSFileController` class. This endpoint uses the `GetMapping` annotation to handle GET requests and returns a list of uploaded files (`KSDocument`) from the `ksDocumentRepository`.
This commit message suggests that a new feature has been added to the codebase, specifically an endpoint to list uploaded files.
