Add grpc starter and httpexchange starter to the community starters document

[DanielLiu1123]

Add grpc-starter and httpexchange-spring-boot-starter to the community starters document.

grpc-starter is a more modern grpc starter, integrating many technologies from the grpc ecosystem. This includes @Autowired support for grpc stubs, proto validation (pgv, protovalidate), metrics, tracing, JSON transcoder, and more.

httpexchange-spring-boot-starter is a starter for Spring 6 declarative HTTP client (Http interface), offering an experience similar to Spring Cloud OpenFeign without the need for annotations like @FeignClient. It supports Spring Cloud LoadBalancer, dynamic refresh, native image, and more.