Add RESO Context to Web API Payloads

[darnjo]

Adding @reso.context to Web API payloads.

There was a prior question about whether we could add the @reso.context for RESO Common Format to Web API payloads as well, so consumers could easily understand them if they already supported RCF. It seems the answer is “yes.” See Control Information from the OData spec.

In addition to the “pure data” a message body MAY contain annotations and control information that is represented as name/value pairs whose names start with @.

Like @reso.context.

In requests and responses with an OData-Version header with a value of 4.0 control information names are prefixed with @OData., e.g. @odata.context. In requests and responses without such a header the “odata.” infix SHOULD be omitted, e.g @context.

I don’t think we want to use something general like @context since it could collide with other annotations. Anything related to @reso like @reso.context can be prefixed with @reso so it’s clear and unambiguous.

In some cases, control information is required in request payloads; this is called out in the following subsections.

Receivers that encounter unknown annotations in any namespace or unknown control information MUST NOT stop processing and MUST NOT signal an error.

This last part is important.