Gradle 8 support

[stewartfrancis]

• Adjusts API usage to remove some internal API usage that was deprecated in Gradle 7 and removed in Gradle 8. There'll be more of this to do for Gradle 9, but I've not done that now.
• Updates tests to run on Gradle 7.6.1 and 8.3, derived from a commit from @ind1go
• Adds a new sample project which demonstrates how to build an OSGi bundle and repackage into a CICS bundle in the same module
• Adds a cicsBundle configuration which could be used to resolve the CICS bundle project by down-stream projects. Does not add a Component so this could be easily published, but that would be a logical next
• Small rewrite of how the tasks are wired together to prevent eager task creation.

I did also notice that we had an unnecessary property on the package task, which I removed. This technically breaks our API, so we may want to consider a major version bump (or just deprecating that property instead of removing it). There are other things we might consider if doing a major version bump anyway, like the changes to how to register additional bundle part configuration that @KyeMaloy97 and I discussed (which I've now forgotten about entirely), and making the tasks usable independently of the project and extensions.

[stewartfrancis]

I've reintroduced the old property, and deprecated it. Also addressed your other review comments (thanks) @ind1go ready for a re-review now.

[ind1go]

Ah, DCO 😑