Support appending to file without read/write access

Search terms you've used

I've searched for "patch" and "append"

Feature suggestion

The Solid rest-api describes that we can use a PATCH request to append data with SPARQL. I would like to see an implementation of this, which allows appending a Thing to a specific file with only append access.

Expected functionality/enhancement

Something along await appendToFile(url, thing). I'm not very familiar to the solid-client API, so there may be a better solution.

Actual functionality/enhancement

Currently it seems possible to update a file only if one has read and write access.

Use Cases

I would use it to let people append themself to secret groups.

Indirectly this allows granting access to a file shareMe.txt via a link:

1. create file myGroup where everbody can append, but not read (so the content is secret)
2. give a group with a cryptographically random name (asdfasdf) access to shareMe.txt
3. create a Link which contains the random name (https://example-sharer.com/#key=asdfasdf)
4. anybody with this link can append themself to group asdfasdf and thus has access to shareMe.txt

Additional information

Start with the Solid REST API PATCH specification linked in the issue and the current file-update entry point in solid-client-js. Clarify how an appendToFile(url, thing)-style operation should work with append-only access, including the expected permission behavior. Done means the library supports the requested append operation without read access and covers its behavior with tests.