Add the spark-library to the classpath for the rest jar in core Gaffer.

[n3101]

Describe the new feature you'd like Add the spark-library to the classpath for the rest jar in core Gaffer.

Why do you want this feature? This will enable gafferpy to access the existing Gaffer Spark Operations.

Describe alternatives you've considered N/A

Additional context Presumably the lack of this library also means the existing Gaffer Java Spark Operations don't work?

[n3101]

#2967 needs to be done before deciding whether to do this one.