fix: add metadata field to CreateCallDTO schema

Add top-level `metadata` field to CreateCallDTO, CreateOutboundCallDTO,
and Call response schemas in the OpenAPI spec. This field was already
present on CreateAssistantDTO and AssistantOverrides but missing from
call-related schemas, causing all auto-generated SDKs (including .NET)
to lack a metadata property on CreateCallDto.

The field follows the same pattern as CreateAssistantDTO's metadata:
a simple object type for storing arbitrary key-value metadata on calls.

Linear: PRO-1773

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Vapi Tasker

fern/apis/api/openapi.json

@@ -34766,6 +34766,10 @@
           "transport": {
             "type": "object",
             "description": "This is the transport of the call."
+          },
+          "metadata": {
+            "type": "object",
+            "description": "This is for metadata you want to store on the call."
           }
         },
         "required": [
@@ -35032,6 +35036,10 @@
                 "$ref": "#/components/schemas/CreateCustomerDTO"
               }
             ]
+          },
+          "metadata": {
+            "type": "object",
+            "description": "This is for metadata you want to store on the call."
           }
         }
       },
@@ -35200,6 +35208,10 @@
                 "$ref": "#/components/schemas/CreateCustomerDTO"
               }
             ]
+          },
+          "metadata": {
+            "type": "object",
+            "description": "This is for metadata you want to store on the call."
           }
         }
       },
@@ -65537,4 +65549,4 @@
       }
     }
   }
-}
+}