Implement GitLab CI to validade PHPCS automatically

Problem/Motivation

Verified that now we can Implement GitLab CI on Drupal.org to validate PHPCS among other validations

The project Tour UI → implemented. E.g.:

• https://git.drupalcode.org/project/tour_ui/-/pipelines
• https://git.drupalcode.org/project/tour_ui/-/pipelines/14541

Proposed resolution

• Follow this documentation →
• Implement first for PHPCS