override type in join__field should use the enum type rather than the graph name.

[clenfest]

Should match the way we reference graphs elsewhere.

[pcmanus]

Fwiw, doing this is not imo worth the potential trouble, as least not as a standalone change.

In principle, I don't disagree that using the enum would be a bit more consequent, but in practice, this doesn't have much practical impact. I get that it can be a one-time minor annoyance to a consistency-conscious reader, but it hardly obscure the meaning either. On the other side, changing this would mean bumping the join spec version and that has a bunch of trickling effects as:

1. the code will need to handle both versions anyway.
2. that's going to add some constraint on upgrade for users (we'll need to tell people to upgrade their gateway first before recomposing) and we'll need to test the hell out of this upgrade.

To be clear, we'll need to change the join spec at some point eventually (and fwiw, I think there is good reason to consider some bigger change in the overall approach of that spec, but that's a completely different discussion) and so we'll need to deal with version upgrade and testing then.

My point is only that doing such work just to correct that very minor inconsistency is not a good use of time/resources. So I guess I'm concretely suggesting here:

• make sense to sneak that change in next time we have an important need for bumping the jump spec;
• but not worth imo until then.