Add documentation for new `colorize` keyword argument in traceback documentation

[mccullerlp]

Documentation of Traceback module colorize features

The new colorized tracebacks are awesome. When users manually create tracebacks using the traceback module, they will not get colorized output by default.

This is because the colorize=True argument needs to be passed to the traceback.print_exception function.

This argument isn't in the documentation. I found it by reading the diffs on the traceback colorization PR.

#112730

[pablogsal]

Unfortunately the reason the code is structured as it is is to keep that argument private to the stdlib. The colorization story is still ongoing so we are not ready to open this for public consumption in case we need to change it in the future. Thanks for your understanding