Add better doc support for multicommands.
Review Request #12133 — Created March 10, 2022 and submitted — Latest diff uploaded
rbt-command-usagedirective in our docs didn't handle the new
multi-commands very well (it would just print "rbt <subcommand>"). This
change extends it to rely on the commands' parser directly for
generating the help message, which improves the usage string, and adds a
list of available subcommands.
Built documentation and looked at the doc for