feat: optionally output to json

[jeremylong]

resolves #62

[jeremylong]

This code is still missing test cases. But I have tested it locally and it appears to work well. I will move this from a draft once I have added test cases.

[jeremylong]

@macblazer I'd appreciate an opinion on this PR. Are you okay with mixing the JSON generation into the single bom_builder class or should there be two builders?

Ideally, to do this would mean re-writing a good portion of the library to generate a model and then use serialization to output the XML or JSON. However, I do not have time to do this.

[macblazer]

I think this approach is acceptable for now. The time involved with refactoring into a model is one of the reasons the original feature request has been sitting for so long.

The cyclonedx-ruby-gem project is also written in Ruby. If there were to be a common Ruby model library for the specification, both this CocoaPods analysis and the RubyGem analysis would benefit from it.

[jeremylong]

Honestly, this code was mostly written using Cody. I've never written any Perl and this is the first Ruby I've touched. CHOP for the win ;)

It might not take very long to convert over to a model based approach using tools like Cody.

[jeremylong]

This PR is good to go now. If this is good enough for now - great. When I have more time I might come back to this and see about converting this to using a model and serialization.

It would be good to see this merged and 2.0.0 released.

[jeremylong]

@macblazer any chance this could get merged a new release created? There are several changes pending the next release:

1.4.1...main

(also - I might suggest using squash-and merge to reduce the noise in the commit history of main)