[sample gen] Sample client method contentType parameter is missing

[v-jiaodi]

spec link: https://github.com/Azure/azure-rest-api-specs/tree/main/specification/appconfiguration/data-plane/AppConfiguration

typespec:

@doc("A key-value model.")
model KeyValue {
  key?: string;
  value?: string;
}

@doc("Put key-value operation")
@route("/kv/{key}")
@put
op putKeyValue(
  @doc("The key parameter")
  @path
  key: string,
  
  #suppress "@azure-tools/typespec-client-generator-core/no-unnamed-types" "Maintaining compatibility"
  #suppress "@azure-tools/typespec-azure-core/no-closed-literal-union" "Maintaining compatibility"
  @doc("Content-Type header")
  @header("Content-Type")
  contentType:
    | "application/vnd.microsoft.appconfig.kv+json"
    | "application/vnd.microsoft.appconfig.kvset+json"
    | "application/json"
    | "text/json"
    | "application/*+json"
    | "application/json-patch+json",
  
  @doc("The key-value to create.")
  @body
  entity?: KeyValue,
): {
  @statusCode statusCode: 200;
  @body body: KeyValue;
};