Support container updates

First off: this issue is different than creating LDPC on route to creating an LDP-RS as a member of an LDPC that doesn't exist yet. That particular case was covered in https://github.com/solid/node-solid-server/pull/513.

This issue is about creating or updating an LDPC (ie an LDP-BC, at the time of this writing). It will conform to LDP provided that the information in the update payload doesn't get in the way of changing the containment triples ( https://www.w3.org/TR/ldp/#h-ldpc-put-mbrprops ). So, for example, adding a label to a container (<> rdfs:label "Foo") would be fine, but PUT/PATCH that inserts or deletes ldp:contains relations should not succeed.

The use cases are generally about including additional "metadata" as part of the container description. It is partly discussed in https://github.com/solid/node-solid-server/issues/547 .

If this feature is implemented, https://github.com/solid/node-solid-server/issues/547 can be revisited, and as far as I can tell, the feature where updating a container's description through /.meta can be removed altogether (as interacting directly with the URI in question would be generally preferable.)

Edit: rel="describedBy" .meta in HTTP header can also be dropped as the interaction will only go through container URI, and that .meta will only be internal to the server.

Beginne damit, die Anforderungen für die Aktualisierung von LDP-Containern und die zugehörige Diskussion in Issue #547 zu prüfen, und ermittle anschließend den Server-Einstiegspunkt, der Aktualisierungen an einer LDPC-URI verarbeitet. Bestimme, wie PUT- und PATCH-Payloads ldp:contains-Tripel im Vergleich zu anderen Metadaten behandeln. Als erledigt gilt die Aufgabe, wenn Container-Metadaten über die Container-URI aktualisiert werden können, ohne Änderungen an der Containment zuzulassen, während das beschriebene .meta-Verhalten nicht mehr benötigt wird.