Use FieldDefCreatorContext for field creation

[aprudhomme]

Add the context class FieldDefCreatorContext to be used by FieldDef implementations during creation. The context currently only contains NrtsearchConfig, but more items can be added as needed.

[sarthakn7]

What else are we planning to add in this context in the future?

[aprudhomme]

What else are we planning to add in this context in the future?

I am going to need some changes to the ExecutorFactory so that it will need to be passed to the vector field through this context. We may also need to pass other services in the future, if we move away from static instances.