doc/eve-format: document row_description fields

Add the pgsql.response fields: row_description_malformed and
field_count to the list, as they're relevant to the patch at hand.

Part of
Ticket: #8885

doc/userguide/output/eve/eve-json-format.rst

@@ -2779,6 +2779,12 @@ pgsql flow. Some of the possible request messages are:
   in a CopyOut transaction
 * "copy_done": string. Similar to ``command_completed`` but sent after the
   backend finishes sending a batch of ``CopyData`` messages
+* "field_count": integer. The number of fields declared by a ``RowDescription``
+  message
+* "row_description_malformed": bool. True when the ``field_count`` declared by a
+  ``RowDescription`` message disagreed with the message body delimited by its
+  length field. The declared ``field_count`` is still logged, as seen on the
+  wire
 * "ssl_accepted": bool. With this event, the initial PGSQL SSL Handshake
   negotiation is complete in terms of tracking and logging. The session will be
   upgraded to use TLS encryption