Add a flag indicating this `Operation` uses `@defer`

[rohandhruva]

Use case

For the auto-generated files that correspond to an Operation, we currently have no way of identifying whether this operation uses @defer. Would it be possible to add a flag that will tell us?

The reason behind this request is that internally we wrap the apollo client APIs, and our current query() API is a suspend fun, which means that it can't support streaming / multiple responses that is required when using @defer.

With this flag, we can fail-fast when someone tries to use our custom suspend fun query() with an operation that uses @defer.

Describe the solution you'd like

Perhaps interface Operation is a good place to add this new flag?

Maybe the flag could be something generic and not specific to @defer, for example: val canHaveMultipleResponses (naming is hard 😅). I'm guessing @stream will need something like this too.