[REQ] Update Java Vert.x Web to use Vert.x 4.2 Constructs

Is your feature request related to a problem? Please describe.

Since this generator was created, the underlying Vert.x mechanisms for Web API Implementation have changed drastically. The old
OpenAPIv3Router has been replaced with the new OpenAPI RouterBuilder. The older ServiceProxy implementation has been updated to use WebApiServiceGen interfaces. It would be helpful if this generator could be expanded to support the newer Vert.x 4.2 semantics.

Describe the solution you'd like

1. The generator should retain backward compatibility for current users
2. The new features should aim to support different reactivity constructs (RxJava2/3, Mutiny, Future, CompletionStage)
3. The generated service interfaces should return a "Not Implemented" response as part of a default method body
4. Generate stubs for the service implementations using the chosen reactivity constructs
5. A generated MainVerticle should use the selected reactivity constructs to initialize, bind, and mount the web API services.

Longer term additional goals:

• Mock implementation
• Authorizations

Describe alternatives you've considered

• I have considered creating a new generator altogether, but that seems to be a confusion solution and there are already multiple Vert.x generators
• Locally, I have created my own override templates which meet my needs, but they are not easily re-usable for others
• I have considered contributing just updated templates, but that will not handle all of the reactivity constructs

Additional context

An example of my customized templates can be seen in the modules/api module of this maven project

Start by reviewing the current Java Vert.x Web generator and the customized templates in the linked Maven project's modules/api module. Clarify the backward-compatibility and reactivity requirements before locating the affected generator templates; done would include the requested Vert.x 4.2 constructs, service stubs, default responses, and MainVerticle generation.