Handle getting Day Ahead forecasts

[devsjc]

The Day Ahead forecast request is a slightly more involved query. The data that is desired is very specific and does not conform to the horizon+window filtering model in the current GetForecastAsTimeseries route. Some thinking needs to be done to determine exactly how this should be implemented.

[peterdudfield]

One option could be we add a DA flag in the forecast value metadata. And then we have an option to filter when we are queries for that flag