Improve CI/CD for documentation website

[naskio]

This PR optimizes the CI/CD workflow for the documentation website:

• Skips deployment steps if GitHub Pages is disabled or the branch is not the default
• Uses yarn consistently instead of detecting the package manager
• Updates to the latest Node LTS version
• Adds a more realistic fallback tag for deployment versioning
• Constrains only the deploy job concurrency
• Triggers the workflow only on changes to the docs/ folder (on push or on pull_request)
• Dynamically set url and baseUrl to allow deploying in forks (for example: https://naskio.github.io/consuldotnet/)