Get our ikiwiki features merged upstream

Estimated time:

- Perl development & upstreaming 20h [xxx]
- Reviewer: 6h [intrigeri]

Parent Task: #15079 (closed)

Related issues

Is duplicate of #15355

Original created by @u on 16435 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information