Add JsonRender and --json command line option

[kimsey0]

We use OpenAPI-diff in a non-Java environment where we want to be able to inspect the generated diff. We currently use a tiny wrapper program that runs OpenApiCompare.fromLocations, then serializes the resulting ChangedOpenApi to JSON using Jackson. It would be useful to us to drop the wrapper and have this functionality built into OpenAPI-diff instead, similar to the built-in Markdown and HTML rendering.

This pull request adds a new JsonRender class and a --json <file> command line option which works similarly to the existing --html, --markdown, and --text commands.

The generated JSON is quite large, and it could be useful to clean-up, for example removing newSpecOpenApi, oldSpecOpenApi, but it's still useful, as long as you parse out the specific parts you need instead of read through the whole thing.

Feel free to make or suggest any needed edits. I do not work too often in Java, so there may be some non-idiomatic parts in the pull request.

[eacolina]

BUMP!💯

[joschi]

@kimsey0 Thanks for your contribution! ❤️

[kimsey0]

@joschi: Might this be released in a beta to Docker Hub sometime? :-)

[joschi]

@joschi: Might this be released in a beta to Docker Hub sometime? :-)

See here:

• Docker image for beta11 missing #269

[kimsey0]

Thanks. I hope you find a solution, whether it's applying for the Docker Open Source program, building images here in GitHub Actions, or something else.