Allow supplying time span for "Raw" assets

[santilland]

Currently we parse the time entry expecting a single datetime string.
Some datasets are aggregations of data over multiple years and users would like to define a time span, as STAC also allows this we should explore how we can best support this.

[lubojr]

Good point, setting a start_time and end_time in generator from config should be quick win.
How urgent is this?
Does the eodash client already understand start_time and end_time?

[santilland]

It somewhat does, so it manages it, in the sense that it works for finding the closest date (i theory) but in the calendar widget right now we only show either the start (or end?) date, not the whole time span.