TT#47024 Use config to document allowed Accept header values

Change-Id: If4c064d36ac0fadc97f5dd193bdafe619494e4e4

lib/NGCP/Panel/Controller/API/Root.pm

@@ -226,6 +226,7 @@ sub GET : Allow {
             fields => $form_fields,
             uploads => $form_fields_upload,
             config => $full_mod->config ,
+            ( $full_item_mod && $full_item_mod->can('config') ) ? (item_config => $full_item_mod->config) : () ,
             query_params => $query_params,
             actions => $actions,
             item_actions => $item_actions,

lib/NGCP/Panel/Utils/API.pm

@@ -281,19 +281,36 @@ sub generate_swagger_datastructure {
         }
 
         if (grep {m/^GET$/} @{ $col->{item_actions} }) {
+            my $action_config = $col->{item_config}->{action}->{GET};
+            my $produces = $action_config->{ReturnContentType}
+                ? ref $action_config->{ReturnContentType} eq 'ARRAY'
+                    ? $action_config->{ReturnContentType}
+                    : $action_config->{ReturnContentType} eq 'binary' ? ['application/octet-stream'] : undef
+                : undef;
             $item_p->{get} = {
                 summary => "Get a specific $entity",
                 tags => ["$entity"],
+                $produces ? ( produces => $produces ) : (),
                 responses => {
                     "200" => {
                         description => "$title",
+                        $produces ? ( content => { map {
+                            $_ => {
+                                schema => {
+                                    $_ ne 'application/json'
+                                        ? (type => 'string')
+                                        : ('$ref' => "#/components/schemas/$entity"),
+                                }
+                            } } @$produces } )
+                        : (
                             content => {
                                 "application/json" => {
                                     schema => {
                                         '$ref' => "#/components/schemas/$entity",
                                     }
                                 },
-                        },
+                            }
+                        ),
                     }
                 }
             };