Make equivalent of /livez and /readyz in gRPC and etcdctl command

[henrybear327]

What would you like to be added?

As discussed and mentioned in the comment, take this commit as a base, and finish the implementation of livez/readyz in gRPC and etcdctl command.

Why is this needed?

Based on the discussions in #16007

[henrybear327]

/cc @siyuanfoundation
/assign @henrybear327

[serathius]

Please note #16007 (comment)

Due to #15402 we are supporting a separating HTTP and GRPC endpoints, and recommend it for production.

[henrybear327]

Please note #16007 (comment)

Due to #15402 we are supporting a separating HTTP and GRPC endpoints, and recommend it for production.

Looks like the HTTP part is completed. I will focus on the gRPC part, and extend the feature to the etcdctl command for now!