feat: add configurable Alt-Svc handler for HTTP/3 alternative service discovery

[Harshal96]

Motivation:

Adds a new AltSvcHandler and AltSvcOptions API for advertising HTTP Alternative Services from Vert.x Web routes.

This enables applications to declaratively send Alt-Svc response headers for configured origins, which is useful for HTTP/3 discovery. For example:

router.route().handler(
  AltSvcHandler.create(
    new AltSvcOptions()
      .addOrigin("http://localhost:8080", "h3:localhost:8443")
  )
);

Fixes #2847

[vietj]

@Harshal96 thanks for the contribution, the code is missing the support of HTTP/2 that works differently than with a HTTP header, I recommend you read the ALT-SVC RFC to learn more about this. For that matter you should look at HttpServerResponse#writeAltSvc method which has been added for this purpose.

[Harshal96]

@vietj done, can you please take a look now?

[Harshal96]

@vietj is this good for another review?

[vietj]

we actually don't need JsonGen annotation here, there is no interested in having a converter for this

[Harshal96]

done

[vietj]

I think we cannot reasonnably maintain such a map because it will never be cleaned from stale connections, so we need to find a way to do that properly.

[Harshal96]

updated to remove stale connections