[BUG] `NewRelic` - `None` type of `identity` is not supported

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/53bed2dccf392c14a412735c38a0f55645812294/specification/newrelic/resource-manager/NewRelic.Observability/stable/2022-07-01/NewRelic.json#L1940

### API Spec version

2022-07-01

### Describe the bug

When deploying a New Relic Monitor instance without `identity`, the backend will return success.
But when deploying a New Relic Monitor instance with `identity.Type = None`, the backend will return `ResourceCreationValidateFailed`.

X-Ms-Correlation-Request-Id: 282d7417-3cae-3138-f2d6-b8b1c781e95c

### Expected behavior

When deploying a New Relic Monitor instance with `identity.Type = None`, the backend should also return success.

### Actual behavior

When deploying a New Relic Monitor instance with `identity.Type = None`, the backend will return `ResourceCreationValidateFailed`.

### Reproduction Steps

Deploy a New Relic Monitor instance with `identity.Type = None`

### Environment

_No response_

Start with the linked NewRelic.json API specification at line 1940 and review how the identity property represents Type=None. Reproduce the deployment described in the issue, then determine whether the specification or the New Relic service needs clarification; done requires an agreed change that makes the expected behavior explicit.

Written by the indexing model from the issue text.