Document handling is streamlined across Projects, Sign, Spreadsheets, and related apps by reducing configurable folder links and using clearer folder terminology. Projects still get dedicated document folders, but task-level document links and the task creation action from Documents are removed, while uploads can now correctly keep project-defined customer defaults.

In this PR we 
* Simplify the documents_project bridge logic and code:
* Update config settings/ documents centralizing feature for 
  documents_spreadsheet, documents_sign, documents_project
* Fix an issue where the project could not define a default `partner`
  for the documents created inside its folder.

See details in included commits.

Task-4298444
Task-4294237

Documents are no longer directly linked to individual projects or tasks through the previous bridge logic. Project document counts now focus on files placed in the project folder, making document organization simpler while removing some task-related document actions.

Simplify the bridges logic and code. See individual commits.

Task-4298444