feat(tests): add JSON Schema test coverage

[jeremyfiel]

This PR adds schema test coverage for the JSON Schema,

this is based on the work in the OAS and Overlay projects by @MikeRalphson and @ralfhandl

The schema tests do not cover JSON Schema 2020-12 keywords as defined by the inputs keyword. All Arazzo specific keywords are covered by the tests.

I've also included markdownlint-cli to clean up the spec file.

[jeremyfiel]

rebased on v1.0.0-dev to resolve conflicts.

[jeremyfiel]

Markdown lint was added and the rebase onto v1.0.0-dev included some recent updates by Frank

I didn't change any wording on it

[ralfhandl]

I would separate these changes into two separate pull requests:

• Markdown formatting
• Schema test coverage

[jeremyfiel]

• stripped out the markdown lint updates
• removed the json version of the schema