Operational Forecasts $expid

As discussed with @kserrade we will start testing auto-nmmb to launch operational forecasts for NMMB/BSC-CTM v2.0.4 and we would like, if possible, to have a reserved "namespace" of expids to clearly identify the experiment as an operational forecast (either in test or in operation).

The idea is to have an oDDD (e.g. o002) experiment identifier and maybe a flag for create in order to have an expid starting with "o" (for operational).
Any other approach would be appreciated @dmanubens

Thanks!