createInContainer
suspend fun <T : SolidResource> createInContainer(webId: String, containerUri: String, resource: T): String?
Creates a member inside containerUri by POSTing, letting the server allocate the child URI — and therefore needing only Append, not Write.
Prefer this over create when writing into a container you were granted Add access to: create PUTs to a fixed URI and needs Write, so it would be refused.
Return
the server-allocated Location, or null if it returned none.