Retry policy supports service-specific retry logic

[Jinming-Hu]

Is your feature request related to a problem? Please describe.

Storage team needs this feature for one of STG94 features.
We need to decide whether or not to retry a response based on a new response header x-ms-copy-source-error-code.

Describe the solution you'd like

Add an optional field into RetryOptions. This field is a lambda function, taking a raw response as parameter. Service sdk can set this field and add some service-specific logic to determine if a response should be retried.

Describe alternatives you've considered

Something similar to ResponseClassifier in .Net SDK
https://github.com/Azure/azure-sdk-for-net/blob/bb90af89e27be84541e142a4ffd648825a2fdbe2/sdk/storage/Azure.Storage.Common/src/Shared/StorageResponseClassifier.cs

Additional context

None

Information Checklist
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[ahsonkhan]

Re-opening since we made RetryPolicy final again, until Storage needs the customization feature: #5771
We'll revisit this for STG98.