[Task] Add empty router result diagnostic documentation

[AlbumenJ]

Related issue #10154 #9826

Status: Documents to be improved

Background: When a user requests the Dubbo interface, due to problems such as registry configuration problems, server status, and routing processing exceptions, no available server addresses are available for the request, and an error is reported.

Solution: Print out the processing process by improving logs such as log output registration center status, routing status, etc. to simplify the troubleshooting process. Currently, there is a lack of corresponding documentation.

[sollhui]

please assgin to me

[cv-prasad]

@AlbumenJ can you please assign this to me