DocGen collapsed sections option cannot be negated

[alnoki]

Per the aptos CLI:

(econia) econia % aptos move document -h

--collapsed-sections
            Whether details should be put into collapsed sections. This is not supported by all
            markdown, but the github dialect. Defaults to true

With the --collapsed-sections option defaulting to true, there is no way to set it as false:

(econia) econia % aptos move document --collapsed-sections=false
error: The value 'false' was provided to '--collapsed-sections' but it wasn't expecting any more values

aptos move document [OPTIONS]

For more information try --help
(econia) econia % 

Hence there is no way to generate DocGen files with uncollapsed sections.

@wrwg @gregnazario @alinush @davidiw