Add bounds?

[aaronspring]

https://confluence.ecmwf.int/display/COPSRV/Guide+to+NetCDF+encoding+for+C3S+providers

lead_bnds, valid_time_bnds, time_bnds

For now user decides whether timestamp represents beginning/center/end of period

[aaronspring]

leadtime_bnds The interval of time between the forecast reference time and the valid time. Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)When boundaries are required, the value of the coordinate must be in the centre of the correspondent time cell boundaries

valid_time_bnds Time for which the forecast is valid. Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)When boundaries are required, the value of the coordinate must be in the centre of the correspondent time cell boundaries