OpenAPI work for MDS

[schnuerle]

Explain pull request

Removing JSON Schema from MDS repository and instead moving to OpenAPI in a new external repository, mds-openapi.

Is this a breaking change

• Yes, breaking

Impacted Spec

Which spec(s) will this pull request impact?

• All

Additional context

To see the most recent development changes to the JSON Schema while the community was working on MDS 2.0, see the snapshot-jsonschema feature branch.

[schnuerle]

Note for this work, references to JSON Schema within each API page will need to be updated with direct links, including general schema references and per endpoint.

[schnuerle]

Note to remove in page references to JSON Schema and update to OpenAPI, fix vehicle data type like on Provider page, add some mention of validation on the MDS home page in a new section, remove paratransit from robots.

[schnuerle]

Merging this now so finalization work can focus on the touch-ups in the release-2.0.0 branch to avoid overlapping conflicts with the feature-openapi branch. This PR looks great for a first pass at moving to OpenAPI for MDS validation.