Add configuration option for assigning the initial server state

There are use-cases where assigning the initial state of unmonitored server is useful. One such case is for setups where the monitoring wrongly guesses the server role that happens with e.g. standalone "read replicas" that get synchronized via ETL methods. These types of servers can be used for offloading analytics queries that are detected and handled by namedserverfilter.

Another use-case for this is for internal profiling of MaxScale itself where it routes traffic to itself through UNIX domain sockets. This makes it possible to both amplify the internal overhead of MaxScale as well as cache results locally in MaxScale via the cache filter.