Support created-notify flag for etcdctl

### What would you like to be added?

A created-notify flag for watch command
Context: https://github.com/etcd-io/etcd/pull/22241#discussion_r3755990658

### Why is this needed?

Similar to the client allow the command line tool to also accep create-notify flag.

Start at the etcdctl watch command and compare its flags with the client-side created-notify option discussed in the linked context. Add the command-line flag and verify that watch accepts and applies it consistently with the client behavior.

Written by the indexing model from the issue text.