MINOR: cli: alphanumerically sort the dump of supported commands

MINOR: cli: alphanumerically sort the dump of supported commands

Like for previous keyword classes, we're sorting the output. But this
time as it's not trivial to do it with multiple words, instead we're
proceeding like the help command, we sort them on their usage message
when present, and fall back to the first word of the command when there
is no usage message (e.g. "help" command).