fix: change ncco websocket endpoint contentType to content-type (#292)

The Vonage Voice Answer API expects a field called "content-type", this model exports a field "contentType". The Vonage Voice API does not recognize this.

Author: rhbuckley

src/vonage/ncco_builder/connect_endpoints.py

@@ -1,5 +1,5 @@
-from pydantic import BaseModel, HttpUrl, AnyUrl, constr, field_serializer
-from typing import Dict
+from pydantic import BaseModel, HttpUrl, AnyUrl, constr, field_serializer, Field
+from typing import Dict, Annotated
 from typing_extensions import Literal
 
 
@@ -29,7 +29,7 @@ class WebsocketEndpoint(Endpoint):
         type: Literal['websocket'] = 'websocket'
 
         uri: AnyUrl
-        contentType: Literal['audio/l16;rate=16000', 'audio/l16;rate=8000']
+        contentType: Annotated[Literal['audio/l16;rate=16000', 'audio/l16;rate=8000'], Field(serialization_alias='content-type')]
         headers: dict = None
 
         @field_serializer('uri')