WIP: chore(@override): add e2e testing of progressive overriding

[metrue]

This PR is trying to validate if the @override behaves correctly when the progressive label applied, because when I trying to move one of my entities from a subgraph to another subgraph, I tried to leverage this progressive overriding to shift the traffic gradually, but the result observed,

• When no label applied, the overriding field will always be resolved in the new subgraph
• When label applied, the overriding field will always be resolved in the old subgraph

I did read the document in Apollo website, and doubled check my schema design for our internal service, I did not find anything wrong, so I am opening this PR to validate @override(from: string, label: string), and you can see the test result proved above conclusion: label not working as expecting, when label applied, the resolving always happens in the old subgraph.

Could someone help review it and explain a little bit if I am doing it correct?

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[metrue]

Confirmed with Apollo team, the progressive feature for @override only supported on Rust router, so it's not possible to use it on federation/gateway out of box.

But if we really need to do it on the federation/gateway, we can do a little hacking in the queryplan building but it will lose the queryplan caching. I tried this commit 1da5e43, now you can see the CI is passed, but obviously it's a thing to try on production.