Applies to both SQL SQLite dialect and GPKG

The ``gdal_get_pixel_value()`` function (added in GDAL 3.7) can be used to extract the value
of a pixel in a GDAL dataset. It requires the configuration option OGR_SQLITE_ALLOW_EXTERNAL_ACCESS
to be set to YES (for security reasons).

It takes 5 arguments:

* a string with the dataset name
* a band number (numbering starting at 1)
* a string being "georef" to indicate that subsequent values will be georeferenced
  coordinates, or "pixel" to indicate that subsequent values will be in column, line
  pixel space
* georeferenced X value or column number
* georeferenced Y value or line number

.. code-block::

    SELECT gdal_get_pixel_value('../gcore/data/byte.tif', 1, 'georef', 440720, 3751320)
    SELECT gdal_get_pixel_value('../gcore/data/byte.tif', 1, 'pixel', 0, 0)