git_ruff: add argument to control terminal text formatting

[SwooshyCueb]

At present, git_ruff.py will format diffs if it thinks it's running in a terminal, and will also format workflow messages if it doesn't detect the presence of the GITHUB_ACTION environment variable. Let's add a --color= argument with the following values:

• force/always: terminal text formatting always on, error if termcolor not available or wrong version
• on: terminal check ignored, only GITHUB_ACTION check performed
• auto (default): current behavior
• off/never: terminal text formatting always disabled