Introduce getProductDependenciesTransformers to ConjureProductDependenciesExtension to help unblock configuration cache

[FinlayRJW]

Before this PR

Previously there was no mechanism for other plugins to safely modify the ConjureProductDependenciesExtension.getProductDependencies this resulted in other plugins just modifying the state of getProductDependencies on the extension directly. This used to work from dumb luck but now we are rolling configuration cache out the convertDependencies method is called before other plugins have a change to modify the state

After this PR

Fundamentally this is meant to be a light touch PR we want to unblock configuration cache without having to do a massive re-write of gradle-conjure at some point we will be force to comeback and make a lot of changes but for now I'm trying to keep it minimal

If we where to build this from the ground up we should have used the NamedDomainContainer but this forces you to change the was you set serviceDependencies in your build.gradle so instead we settled on adding a getProductDependenciesTransformers method on the extension that allows other plugins to add methods that modify the ServiceDependency as late as possible

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Possible downsides?

I couldn't figure out how to get a test working in the IntegrationSpec so I've added a small java test for the extension this can be a FLUP if it is critical

This does introduce a few breaks!

• getProductDependencies and getEndpointVersions are now SetProperties
• ConjureProductDependenciesExtension is abstract

This should not be much of a problem we only seriously use this extension in one internal plugin -> https://pl.ntr/2v9 a PR to fix this there will follow soon

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Description

Introduce getProductDependenciesTransformers to ConjureProductDependenciesExtension to help unblock configuration cache

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[FinlayRJW]

Is this a good enough justification? should I do a separate one for each break?

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