Allow the usage of "-format" with the new method

[peruzzof]

Is your feature request related to a problem? Please describe.
I am planning to use oasdiff not to detect changes, but to compare the designed OAPI with the one generated by the code. But I am expecting some differences, so I need to process the result with another mechanism. And will be easier to do so using the JSON or YAML format.

Describe the solution you'd like
As JSON is easier to deal in a script I will prefer over YAML, but I can work with the 3 options that used to work with the old method.

Describe alternatives you've considered
As the old method is deprecated I hope that this will be implemented before it is removed.

Additional note
As not all flags are common between both methods it will be better if this is clear in the documentation and/or help page.

[reuvenharrison]

Hi @peruzzof,
The "new method" is only relevant to Breaking-Changes.
The diff formats will remain unchanged and will not be deprecated.
I will try to clarify this in the documentation.
Regards,
Reuven