docs(README.md): update links in README.md to GitLab CI/CD documentation for better accuracy and readability

feat(gitlab-ci-php.yml): add support for checking outdated dependencies with composer outdated command
feat(gitlab-ci-php.yml): introduce outdated-enabled variable to control running composer outdated command
feat(gitlab-ci-php.yml): update outdated-args variable description for more clarity

chore(gitlab-ci-php.yml): comment out php-codesniffer, php-sbom, and php-composer-audit jobs to temporarily disable them from the CI pipeline