features: fix the CRS in a request body and the last modification time

[cportele]

Part of addressing ldproxy/ldproxy#1756

• The 'coordRefSys' member of a geometry was passed to the parser as the
  enclosing object, so a JSON-FG geometry with an in-document coordinate
  reference system was rejected with "Expected STRING, OBJECT or ARRAY for
  'coordRefSys', but got: OBJECT".
• The JSON and the GML geometry decoder can be restricted to a list of
  coordinate reference systems; a 'coordRefSys' member or a 'srsName'
  attribute that resolves to another one is rejected. Only the code is
  compared, not the axis order, which is a property of the encoding.
• The last modification time of a feature was parsed with Instant.parse in a
  catch-and-ignore, which fails for every value without a time zone - and a
  DATETIME property is projected as a timestamp without time zone. It is now
  parsed with the same flexible parser as the temporal extent, a value
  without a time zone is interpreted in the provider's 'nativeTimeZone', and
  a value that cannot be parsed at all is logged instead of ignored.
• The source schema validator warns when a DATETIME property is mapped to a
  column with a time zone while 'nativeTimeZone' is set to another zone than
  UTC: the values of such a column are read in UTC and would then be
  interpreted in the configured zone, which shifts them.