Access to the clientMutationId provided to a mutation

[rogerballard]

Is your feature request related to a problem? Please describe. I want my API to cache mutation responses against a clientMutationId.

Describe the solution you'd like I want access to the clientMutationId provided to a mutation so that if my API sees the same clientMutationId twice, it can be certain it is a duplicate call, and return the cached value.

Perhaps exposed via a ClientMutationId parameter decorator.