Document App - enable relative image paths

[jjeroch]

To Do

docs app isn't yet enabled to relative images paths: #220
Enable relative image paths

[MaximilianHauer]

@evegufy do we need this story still ?

[evegufy]

@MaximilianHauer yes, would be nice

[evegufy]

would make step 3 obsolete https://github.com/eclipse-tractusx/portal-assets/blob/main/docs/admin/Dev%20Process/How%20to%20contribute.md#adding-pictures
maintaining absolute links isn't intuitive for contributors. Also, when a PR updates a picture, the picture is currently only resolved once the PR is merge into main, that's again not intuitive.