Fix consistent use of "content" variable

Problem/Motivation

The "content" render array in the project-wiki-entry.html.twig is somewhat unusual, as it has no fields as children. You may want to discuss this with @anybody. I am not sure how to proceed there. The problem is that I can't extract certain fields from the content and print them separately (like author or submitted).

@thomas.frobieter only tested with entity entries, not markdown file content. So there may be other things to work out in the template.
We should always test with both enabled!

So either we should use content as expected or use a different name for that.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes