Overloading of "id" across JSON-LD and RPDE

[nickevansuk]

The "id" property is defined in schema.org / JSON-LD as a URI, however the RPDE spec defines "id" as the native system ID.

schema.org uses "identifier" to reference the native system ID.

This has the potential to create confusion when JSON-LD is embedded in RPDE as there are two "id" properties for the same item with different values.

Should the next version of RPDE use "identifier" instead of "id" for consistency?

[nickevansuk]

Now depends on openactive-archive/opportunity-api#10