cli,helpers: don't always use color

[ee7]

Benefits:

• A user who writes configlet lint > output.txt will no longer see
  color codes in that file.
• It becomes easier to write integration tests for configlet lint.

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Currently when we have a PR that affects configlet lint, I check the diff that the PR makes to the output of configlet lint on every track. This PR helps to simplify that process a little.

From e.g. https://clig.dev/#output:

Disable color if your program is not in a terminal or the user requested it. These things should disable colors:

• stdout or stderr is not an interactive terminal (a TTY). It’s best to individually check—if you’re piping stdout to another program, it’s still useful to get colors on stderr.
• The NO_COLOR environment variable is set.
• The TERM environment variable has the value dumb.