MT#54356 Fix swagger documentation for 'calllist' api

The 'duration' field is reported in the documentation as 'number'
but in fact it is a string, for example: "0:00:16.495".
In the commit the definition of the parameter is changed from
PosInteger to Text

Change-Id: I317006f5bbb5c4b7ffea0abe29dc0b175d8f95e6
(cherry picked from commit 958e40e2ca)

lib/NGCP/Panel/Form/CallList/Subscriber.pm

@@ -118,7 +118,7 @@ has_field 'start_time' => (
 );
 
 has_field 'duration' => (
-    type => 'PosInteger',
+    type => 'Text',
     required => 1,
     element_attr => {
         rel => ['tooltip'],