chore: add .gitlab-ci.yml validation script

What does this MR do and why?

This change adds automatic validation for GitLab CI configuration files to the project's quality checks.

When developers commit or push code that includes changes to the .gitlab-ci.yml file (which controls automated builds and deployments), the system will now automatically run a validation script to check if the configuration is properly formatted and valid. The validation uses GitLab's official command-line tool called "glab" to verify the file, and if the tool isn't installed, it shows a warning but doesn't block the commit.

This helps catch configuration errors early in the development process, before they cause problems in the automated build pipeline, making the development workflow more reliable and preventing broken deployments.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.