Add --black / --no-black options

[akaihola]

Is your feature request related to a problem? Please describe.
It's currently not possible to just run other tools and not Black. Also, in the future, it's desirable to not run Black by default at all.

Describe the solution you'd like
Add the options

• --no-black command line option to skip running Black
• black = false configuration option to skip running Black (unless overridden with --black on the command line)
• --black command line option to override black = false and run Black
• black = true configuration option (the default before Darker 2.0.0)

Describe alternatives you've considered

• Keep Darker as is, and introduce another command line tool which invokes the same code but a different default for the black option.
• Introduce a --format= or --formatter= option.

Additional context

• many-formatters sub-project
• [DESIGN] support different code formatters, allow to skip formatting #304
• Run no formatter by default #450