image push: respect NO_COLOR in aux notes

[WilliamK112]

Summary

• route docker image push aux-note coloring through tui.Output
• respect NO_COLOR when rendering the digest mapping note
• add a regression test covering terminal output with NO_COLOR=1

Why

Fixes docker image push emitting ANSI color codes in aux-note output even when NO_COLOR is set.

Fixes #6890

Testing

• added regression test: TestRunPushRespectsNoColorForAuxNotes
• local static check: git diff --check
• full Go test execution was not available locally in this environment because go is not installed in PATH here; CI should validate compile/test behavior

`docker image push` now respects `NO_COLOR`

[vvoland]

Thanks, your commit sign-off needs a real name though.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[thaJeztah]

Thanks, your commit sign-off needs a real name though.

@WilliamK112 can you fix the sign-off message in the commit to use your real name and e-mail? (Ching Wei Kang) instead of your GitHub handle?

Signed-off-by: WilliamK112 <164879897+WilliamK112@users.noreply.github.com>

Here's some instructions, but let me know if you need more info:

---

We require all commit messages to have a Signed-off-by line with your name
and e-mail (see "Sign your work"
in the CONTRIBUTING.md in this repository), which looks something like:

Signed-off-by: YourFirstName YourLastName <yourname@example.org>

There is no need to open a new pull request, but to fix this (and make CI pass),
you need to amend the commit(s) in this pull request, and "force push" the amended
commit.

Unfortunately, it's not possible to do so through GitHub's web UI, so this needs
to be done through the git commandline.

You can find some instructions in the output of the DCO check (which can be found
in the "checks" tab on this pull request), as well as in the Moby contributing guide.

Steps to do so "roughly" come down to:

1. Set your name and e-mail in git's configuration:

   git config --global user.name "YourFirstName YourLastName"
   git config --global user.email "yourname@example.org"

   (Make sure to use your real name (not your GitHub username/handle) and e-mail)

2. Clone your fork locally

3. Check out the branch associated with this pull request

4. Sign-off and amend the existing commit(s)

   git commit --amend --no-edit --signoff

   If your pull request contains multiple commits, either squash the commits (if
   needed) or sign-off each individual commit.

5. Force push your branch to GitHub (using the --force or --force-with-lease flags) to update the pull request.

Let me know if you need help or more detailed instructions!

[WilliamK112]

Updated the PR commit to use my real-name DCO sign-off and force-pushed the branch. The code/test content is unchanged from the earlier passing run; this update is only to clear the sign-off blocker. Thanks for the guidance.

[thaJeztah]

LGTM

I saw someone also opened a PR with a slightly updated test; #7015 - I'll close or rebase that one after this.

[thaJeztah]

Unrelated to this PR, but we should rewrite the handleAux to get the slice passed in, instead of depending on a package var. For the CLI itself, technically it's not a problem, but the test here shows that we need to manage state now.

I'll have a look at that in a follow-up

[thaJeztah]

No need to fix (I'll have a look at that in the follow-up); this could use t.Context().

DCO was fixed