IStorage apis do not accept cancellation tokens

[colombod]

Orleans.Core.IStorage async apis should require cancellation tokens for consistently

[ReubenBond]

Agreed. We should add optional interface methods since adding a parameter would be a breaking change.

[Chris-Eckhardt]

I started a draft PR to add the optional methods to IStorage. I'm not sure how far we want to go with this PR, I feel like modifying Grain class to use them could lead to some messy changes. Let me know what you think. I'm happy to go in whatever direction ya'll think is reasonable.