Zabbix

.......... [ZBX-23441] renamed AGENT2_CONFIG_PATH -> AGENT2_CONFIG_DIR

This is to bring it in line with the previous change to
AGENT2_PLUGIN_CONFIG_DIR. This does still leave other paths, such as
{EXTERNAL_SCRIPTS,ALERT_SCRIPTS,LOAD_MODULE}_PATH, which I've left alone
for now, to not extend outside Go related things. These should be
updated, however.