feat(33306): Refactor the OpenAPI specs into a Redocly project

[vanch3d]

See https://hivemq.kanbanize.com/ctrl_board/57/cards/33306/details/

The PR refactors the OpenAPI specs of the Edge project in two ways

• relocate the source in its own root directory, ./hivemq-edge-openapi, which will allow its design and modification free of implementation
• bundle the sources into a Redocly project, which provides a set of tools to help you work with OpenAPI definitions

Out-of-scope

• The Redocly tool introduces linting for the OpenAPI specs. There are currently 80+ errors to be fixed. The linting rules of the project (in redocly.yaml) have been changed to reflect the priorities

  rules:
    no-unused-components: error
    ### Custom rules - error must be fixed
    security-defined: off
    no-server-example.com: error

  The errors will be fixed in a subsequent ticket
• The hivemq-edge-openapi is not covered by the recently revamped CI pipeline. A dedicated pipeline, with at least the linting check (see https://github.com/marketplace/actions/redocly-cli-github-action), will be implemented in a subsequent ticket.
• The deprecated file system (in .ext/) has not been removed yet, in order to support a couple of ongoing API changes. The migration will be completed in a subsequent ticket.

[caoccao]

LGTM

[caoccao]

Why MIT? Did we agree on this?