Display max value in the metric name when available

[rjuju]

The function public.list_metrics() should call <wh_name>.list_metrics().

wh_nagios.list_metrics should display the max value when available (i.e. <> 0).

Something like this should be ok :

SELECT * from list_metrics(2);
 id_graph | id_metric |       label        | unit | id_service | available | tags 
----------+-----------+--------------------+------+------------+-----------+------
        2 |         5 | db 1 (max:2053 Mpbs) | Bps  |          3 | t         | {}
        2 |         6 | db 2               | Bps  |          3 | t         | {}