Clarify requirement to base64 encode binary hash value

What does this MR do?

Clarifies the requirement to use the binary SHA256 hash as input to the base64 encoding and provides example input/output values. Response to customer ticket where hex-encoded hash value was being used, and code/utilities being used to perform hashing/encoding did not include Ruby. Providing an example of input and output strings removes potential for incorrect process being used and time spent debugging authentication errors.

Related issues

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