IAV-1044/feat(credentials): add WhatsApp OAuth2 credential type support

Summary

This MR introduces a new WHATSAPP_OAUTH credential type to the credential management system, disambiguating WhatsApp standard API credentials from WhatsApp OAuth2-based credentials.

Changes

mapN8NTypeToCredentialType (reverse mapping — N8N type → internal enum):

Previously, any N8N type string containing "whatsapp" was unconditionally mapped to CredentialType.WHATSAPP. This has been split into two distinct branches:

• If the type contains "whatsapp" but not "oauth" → CredentialType.WHATSAPP
• If the type contains both "whatsapp" and "oauth" → CredentialType.WHATSAPP_OAUTH (new)

mapCredentialTypeToN8NType (forward mapping — internal enum → N8N type):

A new case has been added to the switch statement:

case WHATSAPP_OAUTH -> "whatsAppOAuthApi";

Testing

• Create a credential with type WHATSAPP — should map to whatsAppApi as before
• Create a credential with type WHATSAPP_OAUTH — should map to whatsAppOAuthApi

Related Issues

Closes IAV-1044