[E2E] change node url backend config

[ascjones]

Modifies the e2e configuration for backend node from node_url = "<url>" to backend(node(url = "<url>")).

The previous configuration allowed node_url to be set even if using backend(runtime_only) which uses no node at all so the url is not used at all.

Follows up #2047

[SkymanOne]

Maybe we can make the url an optional param?

- backend(node(url = "<URL>"))
+ backend(node = "<URL>")

[ascjones]

Maybe we can make the url an optional param?

- backend(node(url = "<URL>"))
+ backend(node = "<URL>")

I'm not sure exactly how to achieve that using Darling. Would have to make node a property of Backend, but that is an enum not a struct hence the derive produces the enum(variant) syntax.

I've played around a little bit and can't immediately find a nice way to do that. I'm sure it is possible but I will leave it for now.

[SkymanOne]

Maybe we can make the url an optional param?

- backend(node(url = "<URL>"))
+ backend(node = "<URL>")

I'm not sure exactly how to achieve that using Darling. Would have to make node a property of Backend, but that is an enum not a struct hence the derive produces the enum(variant) syntax.

I've played around a little bit and can't immediately find a nice way to do that. I'm sure it is possible but I will leave it for now.

It is not critical ofc, just nice to have less verbose syntax