Add support for xterm background colors in logs

What does this MR do and why?

This change adds support for background colors in the full log viewer.

Changelog: added

MR acceptance checklist

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Screenshots or screen recordings

Before	After

How to reproduce

php's composer makes use of such ansi backgrounds, so given a command composer validate --verbose --ansi with a faulty config, we can see colorful backgrounds.

Detailed local steps

1. I am using a local shell runner on macos.
2. Installed composer with brew install composer
3. Create a composer project by adding two files:

composer.json:

{
    "name": "group/composer-test"
}

.gitlab-ci.yml

stages:
  - build

composer-validate:
  stage: build
  script:
    - composer validate --verbose --ansi

4. Start my local runner gitlab-runner run
5. Run a pipeline, open the job log, e.g. http://gdk.test:3000/my-group/my-composer-project/-/jobs/2516
6. Visit the job log by adding /viewer e.g. http://gdk.test:3000/my-group/my-composer-project/-/jobs/2516/viewer