"maxctrl alter monitor MyMonitor auto_failover=true" fails

The failover parameter type is an enum now. The enum parameter handling code assumes all valid values are json strings, but MaxCtrl passes "true"/"false" as json booleans and "1"/"0" as json integers. This causes maxctrl alter monitor MyMonitor auto_failover=true to fail. Similarly, "false", "1" and "0" also fail.

Fix by adding a custom version of bool ParamEnum<T>::from_json(const json_t* pJson, value_type* pValue, std::string* pMessage) const for the AutoFailover-type.