Set a "deprecated:true" flag for CLI command generation YAML

[yuandrew]

Instead of having a big string like

      +-----------------------------------------------------------------------------+
      | CAUTION: This command is deprecated and will be removed in a later release. |
      +-----------------------------------------------------------------------------+

for each command that's flagged to be deprecated, it would be easier if we have a deprecated: true flag that can be added to the YAML config, where the parser/generator would append the big string above when generating the command description.