Clarify the usage of DistributedCacheEntryOptions options in the Microsoft.Extensions.Caching.Distributed.IDistributedCache

[tarekgh]

The DistributedCacheEntryOptions options is been passed as a parameter to multiple methods of the IDistributedCache interface. It is not clear in the docs how options should use? should it be used as read-only and not mutated? or should allow mutating it. The contract doc should be explicit about that.

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