Integrate public part of TechDoc

Selected parts of Techdoc may be made available directly unter hifis.net/doc.

• Define publishable parts in Techdoc Gitlab Project @jandt-desy
• Possibly change paths in production build to /doc/, while pointing to https://hifis.pages.hzdr.de/hifis-technical-documentation/ in review apps @frust45
• Similarly, in techdoc project, paths in production should refer to /doc/ @frust45
• Copy (better: CI/CD) master artifacts to hifis.net/doc @jandt-desy