Filter unmodeled fields from error output

[AndrewAsseily]

Description of changes: The CLI's "Additional error details" section previously displayed all fields from the error response, including fields not defined in the service model. This change filters the output to only show fields that are explicitly defined in the service's error shape model.

Non-modeled: https://github.com/aws/aws-cli/blob/v2/awscli/botocore/data/s3/2006-03-01/service-2.json#L8516

Before:

(.venv)  aws-cli % aws s3api get-object --bucket not-a-real-bucket-0000 --key file.txt out.txt

aws: [ERROR]: An error occurred (NoSuchBucket) when calling the GetObject operation: The specified bucket does not exist

Additional error details:
BucketName: not-a-real-bucket-0000

After:

(.venv)  aws-cli % aws s3api get-object --bucket not-a-real-bucket-0000 --key file.txt out.txt                          

aws: [ERROR]: An error occurred (NoSuchBucket) when calling the GetObject operation: The specified bucket does not exist

Modeled: https://github.com/aws/aws-cli/blob/v2/awscli/botocore/data/lambda/2015-03-31/service-2.json#L7930

(.venv) aws-cli % aws lambda get-function --function-name nonexistent-function-12345

aws: [ERROR]: An error occurred (ResourceNotFoundException) when calling the GetFunction operation: Function not found: arn:aws:lambda:us-west-2:<redacted-for-this-PR>:function:nonexistent-function-12345

Additional error details:
Type: User

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