HDDS-7230 implements the GetKeyInfo with the ability to assume S3 volume context by OM. That releases S3G from having to call `getS3VolumeContext` prior to calling `lookupKey`, as it does today.
- S3G Get Key API to call GetKeyInfo via RpcClient with `assumeS3Context=true` ( and without a `volumeName`). S3G doesn't need to call GetS3VolumeContext prior to GetKeyInfo.
- RpcClient once it sees an S3 context in the GetKeyInfo response, takes the user principal, and sets it to the S3LocalAuthContext.
That will reduce once roundtrip between S3G and OM for every GetKey API request.