Add restJson1 protocol test for content-type and operation with no input

[haydenbaker]

Background

• Requests should not have the content-type header added when there is no input shape (and therefore no payload)
  • This doesn't appear to be a case in the aws sdk (operations with no input), but could be in generic clients

Testing

• Tested by running protocol tests in the typescript sdk

Links

• Related to https://github.com/smithy-lang/smithy-typescript/pull/1304

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