simplify mapping to seasonal or diurnal databases

[muelleram]

Currently databases are linked to a specific point in time: e.g. 2020 or 2020-01-01 12:00 am and are then matched based on temporal closeness (closest or linear interpolation between closest neighbors). For seasonal or diurnal analysis, we want to draw from the database that represents best the time within the year or within the day.

Here we should add a function to map to the specific database based on season/diurnal time instead on temporal closeness.