Clarify use of @Core.ContentId in delta update

Add the same text to "Update a Collection", where we describe delta updates, as we currently have in sections describing deep insert and deep update. Note that the DeepInsert and DeepUpdate capabilities that describe support for ContentId should be relevant within a delta update request. Proposed wording: Clients MAY associate an id with individual nested entities in the request by using the Core.ContentID term defined in [OData-VocCore] . Services that respond with 200 OK SHOULD annotate the entities in the response using the same Core.ContentID value as specified in the request. Services SHOULD advertise support for updating a collection using a delta payload using the DeltaUpdateSupported property of the Capabilities.UpdateRestrictions vocabulary term, and SHOULD advertise support for returning the Core.ContentID in the response to a delta update through the Capabilities.DeepUpdateSupport term, both defined in [OData-VocCap] .