Validation and filter feature

There have been a number of issues reported (linked in #882) where it seems that user's data files have been corrupted. Some of these things should be fixed on the frontend, so that it makes sure invalid data is not sent. However, the backend should also check, e.g. by doing a RDF validation as suggested in #882, but we could also imagine SHACL validation, etc. If Inrupt becomes a large POD provider, it may also come with legal requirements.

Also, validation may not only be a boolean accept or error, but possibly also filtering to accept valid parts. For v.next, we need to have an architectural element that does this, but we may need to address parts of this problem already for 5.0.0.

Consider this a super-issue for discussing what should be in 5.0.0, and if we should try to make that reusable in v.next. Also, we may discuss if we do not attempt to solve it on the backend and refer to frontends to do it.

先閱讀 #882 中連結的報告，以及關於 RDF 和 SHACL 驗證的討論。釐清驗證應在前端、後端或兩者中進行，並定義 5.0.0 與 v.next 的範圍。完成的標準是就可重複使用的架構達成共識，並明確定義拒絕或篩選無效資料的需求。