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.

Empieza revisando los requisitos de actualización de contenedores LDP y la discusión relacionada en el issue #547; después, localiza el punto de entrada del servidor que gestiona las actualizaciones de una URI de LDPC. Determina cómo los payloads de PUT y PATCH tratan los triples ldp:contains frente a otros metadatos. Se considera terminado cuando los metadatos del contenedor puedan actualizarse a través de la URI del contenedor sin permitir cambios en la contención, mientras que el comportamiento de .meta descrito ya no sea necesario.