Windows Terminal supports truecolor, but colored doesn't detect that

[spenserblack]

See microsoft/terminal#11057

We could either detect if Windows Terminal is running by checking if the WT_SESSION environment variable exists, or we could wait for Windows Terminal to set the COLORTERM variable.

[spenserblack]

BTW, when looking into this, I realized we support truecolor but not 256-color (I actually just recently realized they're 2 different things). See how GitHub's CLI detects support:
https://github.com/cli/cli/blob/e6ff77ce73c201b0ee36d2b802ea45e9e1ad1822/pkg/iostreams/color.go#L36-L50

If it's worth doing, we could rename TrueColor to Rgb, and print the truecolor or 256-color escape sequence depending on support. If so, I can open a new issue.