gnd: Fix `add` and unify subgraph scaffolding generators #11904

Job	Run time
Run unit tests	3m 23s
Build in release mode	1m 40s
Check rustfmt style	31s
Clippy linting	2m 1s
Run integration tests	4m 40s
Subgraph Runner integration tests	2m 49s
	15m 4s

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