Add support of sending object and other unknown types in header

[asadali214]

Currently the following interface of RequestBuilder defines a header function that only support types string | boolean | number | bigint

export interface RequestBuilder<BaseUrlParamType, AuthParams> {
  ...
  header(name: string, value?: string | boolean | number | bigint | null): void;
}

This does not include the types like object or unknown. Please update this function to allow the support of all kind of header parameters