core/http needs to allow for additional http services to be spun up

[toddself]

Describe the feature:

The core http service needs to allow plugins to spin up additional http services on alternate ports.

If the main https service is TLS-enabled, the secondary services should also inherit that TLS configuration.

Describe a specific use case for the feature:

The proxy plugin #36709 requires that internal communication between kibana nodes be done via a secondary port/service for future compatibility reasons

[toddself]

@restrry this looks like the HttpServer class can be instantiated already with a separate port.

It looks like a plugin could just configure a second http server and start it up, and then we could register the routes for a given resource when the plugin notifies the proxy that it is responsible for a given resource?

Does this sound like a valid strategy