STACIT: add a OVERLAP_STRATEGY opening option to determine how to …

[rouault]

…handle sources fully overlapping others, and taking into accout nodata values

-  .. oo:: OVERLAP_STRATEGY
      :choices: REMOVE_IF_NO_NODATA, USE_ALL, USE_MOST_RECENT
      :default: REMOVE_IF_NO_NODATA
      :since: 3.9.1

      Strategy to use when the ItemCollections contains overlapping items, and
      that some items are fully covered by other items that are more recent.

      Starting with GDAL 3.9.1, the ``REMOVE_IF_NO_NODATA`` strategy is applied
      by default. The STACIT virtual mosaic will omit fully covered items,
      only if no band declares a nodata value.
      (Note that the determination whether a band has a nodata value of not is
      done by opening one of the items, and assuming it is representative of
      the characteristics of the others in the collection).

      This strategy can be forced in all cases by selecting the ``USE_MOST_RECENT``
      strategy (this was the strategy applied prior to 3.9.1)

      The ``USE_ALL`` strategy always causes all items to be listed in the virtual
      mosaic, with the most recent ones being rendered on top of the less recent ones.