Add @LocalContextValue for access to attributes from the local GraphQLContext in DataFetchingEnvironment

[andimarek]

I think it would be useful to have a @LocalContext annotation to allow for the local context to be injected in annotated methods.

Thoughts?

[rstoyanchev]

In light of the planned improvement under #354, I am closing this for now since a local context value can be accessed through @ContextValue, but we can always re-open it if needed.

[rstoyanchev]

Re-opening, given the direction taken with #354.

[rstoyanchev]

In summary, there is now @ContextValue and @LocalContextValue, each binding from the main or the local GraphQLContext respectively. That means existing code accessing the local context will now have to switch to @LocalContextValue.