Update the sample configuration file to properly document discovery v3options with correct nested structure and comprehensive comments.Changes:- Add properly structured discovery-config section with nested YAML- Document all discovery v3 client configuration options- Add default values in comments for timeout fields (in nanoseconds)- Include important notes about duration format requirements- Add security and authentication configuration options- Clarify that only one of initial-cluster, discovery-srv, or  discovery-config can be used- Add CAUTION warning for insecure-skip-tls-verify optionThis addresses the common misconfiguration issue where users attemptto use flat discovery-* fields at the top level, which are silentlyignored in YAML config files. The flat fields only work as command-lineflags, while YAML requires the nested discovery-config structure.Fixes the documentation gap identified when investigating whydiscovery-token and discovery-endpoints were not being parsed fromYAML configuration files.Signed-off-by: xadips <ricardas.cubukinas@vinted.com>