fix: add NO_COLOR support to the config wizard

[tconbeer]

Closes #552

What are the key elements of this solution?
We check the NO_COLOR env var before setting the colors/style for the config app.

Why did you design your solution this way? Did you assess any alternatives? Are there tradeoffs?
Considered deeper support, including a HARLEQUIN_NO_COLOR variable, but it didn't seem necessary. Textual and rich-click already have robust NO_COLOR support.

Does this PR require a change to Harlequin's docs?

• No.
• Yes, and I have opened a PR at tconbeer/harlequin-web.
• Yes; I haven't opened a PR, but the gist of the change is: we should note that we support NO_COLOR somewhere.

Did you add or update tests for this change?

• Yes.
• No, I believe tests aren't necessary. (the config app doesn't have any tests -- I tested this manually.)
• No, I need help with testing this change.

Please complete the following checklist:

• I have added an entry to CHANGELOG.md, under the [Unreleased] section heading. That entry references the issue closed by this PR.
• I acknowledge Harlequin's MIT license. I do not own my contribution.