Add Rule 127 - Use JSON as payload data interchange format

[vadeg]

Implement Rule 167

• Add support for the acceptance list of media types

Fixes #1217

[tkrop]

I'm not sure, but may be this implementation is going to far, since we explicitly relax this rule in #168.

[vadeg]

@tkrop thanks for the comment. My impression was that in these cases API designers have to exclude Rule 167 explicitly. From API perspective it is hard to distinguish where should be JSON and where something else.

[tkrop]

@vadeg Yes, I agree. Excluding rules is definitely an option. However, currently we do not encourage the usage of x-zally-ignore to prevent users from freely applying it to other rules too. I think we should carefully consider the impact of such a strategy change.

[vadeg]

Let's discuss this on our meeting.

[vadeg]

We decided not to implement this rule, because this would lead many exceptions and it would be difficult to validate each case.

[tkrop]

May be you can separate 38da19a, so that we can merge this quickly.

[tkrop]

The build seems to be failing because of the same reason as in #1227:

--- FAIL: TestIntegrationWithNoMustViolations (0.36s)
    integration_test.go:84: 
        	Error Trace:	integration_test.go:84
        	Error:      	Should be zero, but was 17
        	Test:       	TestIntegrationWithNoMustViolations
        	Messages:   	No MUST violations expected
    integration_test.go:88: 
        	Error Trace:	integration_test.go:88
        	Error:      	Expected nil, but got: &domain.AppError{e:(*errors.errorString)(0xc000182c00), c:3}
        	Test:       	TestIntegrationWithNoMustViolations

[vadeg]

May be you can separate 38da19a, so that we can merge this quickly.

@tkrop this has been merged in #1222 . I will update this PR to remove this change.

[tfrauenstein]

hint: we discussed / decided the topic in the API guild meeting --> see https://docs.google.com/document/d/1NahSuMC0LRwFTTrln2m0iDLq0nHzGmF59Gv7xBhKPfQ/edit#bookmark=id.p63ihhuscg86

[ePaul]

Instead of this, we want #1316.