GeoJSON: add a FOREIGN_MEMBERS=AUTO/ALL/NONE/STAC open option

[rouault]

-  .. oo:: FOREIGN_MEMBERS
      :choices: AUTO, ALL, NONE, STAC
      :default: AUTO
      :since: 3.11.0

      Whether and how foreign members at the feature level should be
      processed as OGR fields:

      - ``AUTO`` mode behaves like ``STAC`` mode if a ``stac_version`` member is found at
        the Feature level, otherwise it behaves as ``NONE`` mode.

      - In ``ALL`` mode, all foreign members at the feature level are added.
        Whether to recursively explore nested objects and produce flatten OGR attributes
        or not is decided by the ``FLATTEN_NESTED_ATTRIBUTES`` open option.

      - In ``NONE`` mode, no foreign members at the feature level are added.

      - ``STAC`` mode (Spatio-Temporal Asset Catalog) behaves the same as ``ALL``,
        except content under the ``assets`` member is by default flattened
        as ``assets.{asset_name}.{asset_property}`` fields.

[coveralls]

coverage: 69.935% (+0.006%) from 69.929%
when pulling e4fe405 on rouault:geojson_FOREIGN_MEMBERS
into 42ca02c on OSGeo:master.