Fix meanwhile broken links to helmholtz.cloud

After deployment of -next cloud portal, several old links broke. Some leading to a unfiltered service page, some leading to 404.

Fixing that as far we have the links under control.

Similar/related MR:

• hifis-technical-documentation!396 (merged)
• https://codebase.helmholtz.cloud/hifis/overall/communication/overview-materials/-/merge_requests/28

Newsletter PDFs will remain uncorrected, though...