Provide a json array token (Baleen support)

Here the MR and the patch.

The new token should only be used with the content type application/json to avoid escape chars. Maybe this behavior should be extended to all purger's body?

It should also fix, the todo in buildFormTokensHelp about token auto detection (there a lack of doc bout the core token api).

You probably want to submit it as a merge request: patch format has been deprecated for quite some time already.

The MR is already done, I just added the patch so it can be added safely into compose.json (the MR link could be altered by additional commit, it's still an global issue: https://www.drupal.org/docs/develop/git/using-gitlab-to-contribute-to-dr... → ). I'll edit the message for clarity.

Please test the MR or patch

The patch is live on an production drupal. So far it seems ok
Could some else tests it and marks this issue as RTBC if ok?