Azure Event Grid Using a System-Assigned Managed Identity Example

**What content needs to be created or modified?**

I have looked at the [Event Grid binding spec](https://docs.dapr.io/reference/components-reference/supported-bindings/eventgrid/) but do not understand which fields are or are not required when using a managed identity.

**Describe the solution you'd like**

I would love to see an example for an Azure Event Grid binding using a managed identity.

**Where should the new material be placed?**

I believe it would be best to place it in [Event Grid binding spec](https://docs.dapr.io/reference/components-reference/supported-bindings/eventgrid/).

**The associated pull request from dapr/dapr, dapr/components-contrib, or other Dapr code repos**

**Additional context**

No additional context - just, thank you!