refs #7707
- be able to add a custom redirect file into the content folder
- define redirects as JSON format
The redirects feature is already present in the LTS branch.
I was not able to cherry-pick over, too many changes or conflicts.
Creating a PR to ensure 1. tests pass and 2. overview of code changes.
I had to add an example active theme to our test fixture utils, because otherwise Ghost will complain when forking Ghost.
