[FR] Support for defaultSupportedIdpConfigs

**Is your feature request related to a problem? Please describe.**
The REST/GRPC API provides the ability to manage defaultSupportedIdpConfigs, however, this doesn't seem available from the Admin SDK. Please could you add support for these types of IDPs.

**Describe the solution you'd like**
Similar to being able to manage SAML and OIDC providers, please add into the SDK methods for managing default supported idp configs.

**Describe alternatives you've considered**
Calling the REST/gRPC APIs separately but this involves having to handle all the API handling framework already being completed by the Admin SDK.