Create a IDL based class to store the following operation context metadata:

• Command's comment: this would be an optional BSONObject
• Impersonation metadata: this would be two mandatory vectors one for UserName and the other for RoleName

The constructor of this class would accept an opCtx and will extract these metadata from it. Additionally the class should provide a method that will restore these metadata on a given opeartion context.

An instance of this PassthroughOpContextMetadata will be stored in the ShardingDDLCoordinator