caddy-frontend: Mark TODO entry done

Since caddy-frontend: Support wildcards the wildcards are supported.

software/caddy-frontend/TODO.rst

 Generally things to be done with ``caddy-frontend``:
 
- * support wildcard domain in ``custom_domain`` and ``server-alias``
  * return warning on not implemented keys (from ``apache-frontend`` perspective) in master and slave request
  * tests: add assertion with results of promises in etc/promise for each partition
  * check the whole frontend slave snippet with ``caddy -validate`` during buildout run, and reject if does not pass validation