wcst_import - FIX - Implement areasOfValidity with next_slice support

[Bang Pham Huu]

For coverage with many slices this results in a large DescribeCoverage, e.g. see ​this example:

<ras:areasOfValidity>
<ras:area start="1950-01-01T00:00:00.000Z" end="1950-01-31T23:59:59.999Z"/>
<ras:area start="1950-02-01T00:00:00.000Z" end="1950-02-28T23:59:59.999Z"/>
<ras:area start="1950-03-01T00:00:00.000Z" end="1950-03-31T23:59:59.999Z"/>
<ras:area start="1950-04-01T00:00:00.000Z" end="1950-04-30T23:59:59.999Z"/>
<ras:area start="1950-05-01T00:00:00.000Z" end="1950-05-31T23:59:59.999Z"/>
<ras:area start="1950-06-01T00:00:00.000Z" end="1950-06-30T23:59:59.999Z"/>
<ras:area start="1950-07-01T00:00:00.000Z" end="1950-07-31T23:59:59.999Z"/>
<ras:area start="1950-08-01T00:00:00.000Z" end="1950-08-31T23:59:59.999Z"/>
<ras:area start="1950-09-01T00:00:00.000Z" end="1950-09-30T23:59:59.999Z"/>
...

To make it more convenient we should implement support for next_slice semantics with low/high bounds

Optional low and high can be added (by default they are first direct position and infinity respectively):

"directPositions": ["2024-01-01", "2024-03-01"]
"validity": {"type": "next_slice", "low": "2023-12-01", "high": "2024-12-31"}

equivalent to

"directPositions": ["2024-01-01", "2024-03-01"]
"areasOfValidity": [{"start": "2023-12-01", "end": "2024-03-01"}, {"start": "2024-03-01", "end": "2024-12-31"}]

[Peter Baumann]

Ticket retargeted after milestone closed