Allow regex/wildcards for vfs.files.exists

We are planning to migrate our current monitoring tool to zabbix but one major blocker is that Zabbix does not play well with wildcards using vfs.files.exists. A large number of our systems generate application logs where our current tool would monitor and report if found. It is actually a simple "search for anything .log or error-.log in path /this/path/to/logfile", which does not appear to work with Zabbix vfs.files.exists item.