Add global discovery and load balancer types

[Vincent Sevel]

Support global defaults for discovery and load balancer types used across the application:

stork.service-discovery=consul
stork.service-discovery.refresh-period=7M # default value for consul's discovery param refresh period
stork.load-balancer=least-response-time

# hello will use consul and least-response-time by default
hello/mp-rest/url=stork://my-service/hello

# if needed, params can still be used at the service level
stork.my-service.service-discovery.refresh-period=10M # override global default
stork.my-service.service-discovery.application=myapp

# or use an entirely new discovery/load balancer for a specific service
stork.my-service2.service-discovery=kubernetes

[Clement Escoffier]

Followed up by quarkusio/quarkus-upstream-roadmap#4.

organization: QuarkusIO
repository: quarkus-upstream-roadmap
issue: 4
url: quarkusio/quarkus-upstream-roadmap#4