[FIX] Fix broken links due to missing site_url on mkdocs.yml

Description

Icons and other images are not displayed due to broken links caused by missing site_url on mkdocs.yml

Other Changes

• none

Screenshots/Logs

Testing Instructions

1. Run mkdocs build with updated mkdocs.yml → check mkdocs replacements during build
2. Run analyser on current deployed unicado website → take a look at a specific icon or image which is currently not displayed correctly.
3. Insert in analyser mode the correct path for an image → /unicado.gitlab.io/assets/.... → icon should be displayed correclty on current page. Comparing to replaced site: links from site_url's here correct now.

Developer Checklist

• Code has been tested locally and /or in pipeline (see workaround since local browser are secure against loading content from filesystem, e.g. when run build).
• (if applicable) documentation updated. → not applicable
• (if applicable) impact of new dependencies reviewed and included in project. → no interaction seen
• Merge conflicts resolved with the target branch.

Additional Notes

Make sure to keep site_url updated when location changes!