IdentityProviderRepresentation config map is replaced instead of merged during patch

### Current Behavior

When importing an existing Identity Provider, updating only a subset of its properties causes the existing `config` map to be cleared.

The existing configuration is removed, resulting in something equivalent to:

```yaml
identityProviders:
- alias: oidc
enabled: false
config: {}
```

### Expected Behavior

Only the `enabled` property should be updated.

The resulting Identity Provider should remain:

```yaml
identityProviders:
- alias: oidc
enabled: false
config:
clientId: example-client-id
clientSecret: example-client-secret
tokenUrl: https://example.com/protocol/openid-connect/token
```

### Steps To Reproduce

```markdown
Assume the Identity Provider already exists in Keycloak with the following configuration:

identityProviders:
- alias: oidc
enabled: true
config:
clientId: example-client-id
clientSecret: example-client-secret
tokenUrl: https://example.com/protocol/openid-connect/token

Now import the following configuration:

identityProviders:
- alias: oidc
enabled: false
```

### Deployment Method

Docker

### Environment

- Keycloak Version: 21.1
- keycloak-config-cli Version: 6.5.1
- Java Version: 21

### Relevant configuration (sanitized)

```yaml

```

### Logs / error output

```shell

```

### Anything else?

_No response_