refacto on YAML config pages

[flovntp]

• split YAML doc pages between Upsun and P.sh
• adding YAML structure for Upsun
• solving small display issues
• YAML structure for P.sh
• change binary example (still displaying properties)
• (Option) change link to the generic guide instead of the Express guide: /get-started/express.html#configure-your-project

Why

Closes #{ISSUE_NUMBER}

What's changed

[github-actions]

Your Platform.sh environment has successfully deployed. 🚀

See the changed pages:

• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/learn/overview/yaml/yaml-structure.html
• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/create-apps/multi-app/project-structure.html
• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/learn/overview/build-deploy.html
• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/learn/overview/get-support.html
• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/learn/overview/philosophy.html
• https://fix-yaml-structure-rrrdhxi-ucq44jg6ofare.eu-5.platformsh.site/learn/overview/yaml/platform-yaml-tags.html

[flovntp]

please check all of the pages below YAML section

• some small improvement on config file name in the folder structure schema on all pages in the /overview and in create-apps/multi-app/project-structure.html
  before, it was

├── .upsun
 │           ├── .upsun/config.yaml