shenyu modify dubbo plugin configuration based on selector

complete task 4 in #5923 , modify dubbo registry config base on selector.

i add one parameter "registry" in dubbo selector, and change "protocol" to not required.
for example, change the shenyu-examples-apache-dubbo-service's dubbo.registry.address to 'nacos://localhost:8848?namespace=local_test&username=nacos&password=nacos' if the dubbo selector parameter registry is empty, it will use the default plugin config. i add a common method to get the dubbo ReferenceConfig<GenericService> in ApacheDubboProxyService.java#getReferenceConfig when invoke the api 'http://localhost:9195/dubbo/findById', it will throw No provider exception.
set the dubbo selector parameter to 'nacos://localhost:8848?namespace=local_test&username=nacos&password=nacos' when invoke the api the 'dubboUpstreams' is not empty in ApacheDubboProxyService.java#getReferenceConfig then chose one upstream and create a new ReferenceConfig<GenericService> with a new cacheKey finally, it will use the new ReferenceConfig<GenericService> to invoke the dubbo interface through the new registry。
when build the ReferenceConfig<GenericService> in ApacheDubboConfigCache.java, it will use the new dubbo RegistryConfig and the dubbo rule config is not used in default model. so i wrote a new buildReference method。 And when use the multi registry or there are multiple Dubbo instances, the custom dubbo LoadBalance ApacheDubboGrayLoadBalance will be triggered, so when build the ReferenceConfig<GenericService> i didn't use reference.setLoadbalance("gray") and methodConfig.setLoadbalance("gray").