Identity: `create_oauth2_credential_provider` only supports custom config, not provider-specific configs

## Description

When using `create_oauth2_credential_provider`, users cannot provide provider-specific configurations such as `googleOauth2ProviderConfig`, `slackOauth2ProviderConfig`, etc. Only the custom configuration is supported.

## Steps to Reproduce

1. Attempt to create an OAuth2 credential provider with a provider-specific config (e.g., Google, Slack)
2. Observe that only the custom config option is available

## Expected Behavior

Users should be able to specify provider-specific OAuth2 configurations (e.g., `googleOauth2ProviderConfig`, `slackOauth2ProviderConfig`) when creating a credential provider.

## Actual Behavior

Only the custom configuration is accepted. Provider-specific configs are not supported.

## CLI Version

_N/A_

## Operating System

macOS