Add CLI option to switch true colors on/off

[spenserblack]

Allows user to control if onefetch should attempt to write true colors to the terminal.

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I found myself wanting to turn off true colors when executing onefetch so that the output would match my preferred color scheme, and figured that other users might want to do the same 🙂

[o2sh]

You're absolutely right, for those who like to play with their terminal's color scheme, this flag can come to be very handy.

My only suggestion would be to use --show-logo as a template for its declaration as the two flags seem to operate similarly.

[spenserblack]

My only suggestion would be to use --show-logo as a template

Nice catch! The args should definitely have consistent usage. Suggestions committed.