cli/parser: allow options to be hidden

[Rylan12]

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Allows options to be marked with hidden: true to hide them from brew help, manpages, and completions.

I went with hidden instead of undocumented because it looks like @MikeMcQuaid started to work on this a bit in #11075 and added a seemingly useless hidden keyword argument to the flag method. For compatibility (even though there's likely no one using it as it didn't do anything) I stuck with that. Another more minor benefit to hidden is that it won't require shifting the other arguments in the switch/flag/comma_array method call because hidden is fewer characters than description while undocumented is more.

I've also marked the --bottle flag of brew info as hidden.

[BrewTestBot]

Review period will end on 2021-06-10 at 02:05:58 UTC.

[MikeMcQuaid]

Great work, thanks @Rylan12!

[BrewTestBot]

Review period skipped due to critical label.