Add php-horde ecosystem to security-support-ended.12
Following discussion with the Debian Horde Maintainers and the LTS Team, we request to mark all php-horde* packages EOL for Debian 12 bookworm, as it's currently not in a usable state, mostly due to PHP8 incompatibility. See the provided link for details.
(We also issued a RM request, but that's actually removing 121 packages mid-release and probably won't succeed. Until that happens let's clarify and EOL.)