Allow extra fields in test messages

[erinknight242]

As it is currently implemented, we were assuming that a user would not include "extra" fields in test messages. If you do include a field in your message that is not in the contract definition, it will be considered invalid:

However, it will be a much more common scenario that a producer that has 10 fields will need to satisfy multiple consumer's contracts. They may only have one message created, and they will test each of those contracts against that same message. If all fields of the contract are included in the message, it should be valid and pass. If there are additional fields in the message that exceed the definition of the contract, they can be safely ignored, so we should not see the error above.

Instead, we can display that information as a warning; but still return a 200 code.

Update existing tests to match the new expected behavior, and update the TestMessage logic to allow extra fields in a message that are not in the contract.

[erinknight242]

Example mockup of warning display: