KeyRing and CMM get the original DDB request object through GetEncryptionMaterialsInput / OnEncryptInput / GetDecryptionMaterialsInput / OnDecryptInput

In S3EncryptionClient we are able to access `ExecutionAttributes` added to the AwsRequest object through this. We want to follow the same format for DDB here so we can pass state per request through ExecutionAttributes , per request call.

Start by tracing GetEncryptionMaterialsInput, OnEncryptInput, GetDecryptionMaterialsInput, and OnDecryptInput, then compare how S3EncryptionClient exposes ExecutionAttributes from the original AwsRequest. Done means the original DDB request object and its per-request ExecutionAttributes are available through the corresponding materials and encrypt/decrypt callbacks.

Written by the indexing model from the issue text.