Add support for device identity operations (#142)

* Initial work on identities for modules and devices

* Add create/update device identity feature

* Add missing docs to all enums/structs members and derive default for DeviceCapabilities

* Fix formatting

sdk/iothub/examples/device_identity.rs

@@ -0,0 +1,56 @@
+use iothub::service::identity::{DesiredCapability, Status};
+use iothub::service::ServiceClient;
+use std::error::Error;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    let iothub_connection_string = std::env::var("IOTHUB_CONNECTION_STRING")
+        .expect("Set env variable IOTHUB_CONNECTION_STRING first!");
+
+    let device_id = std::env::args()
+        .nth(1)
+        .expect("Please pass the device id as the first parameter");
+
+    println!("Getting device twin for device '{}'", device_id);
+
+    let service_client = ServiceClient::from_connection_string(iothub_connection_string, 3600)?;
+    let device = service_client
+        .create_device_identity()
+        .device_id(device_id)
+        .authentication_using_sas(
+            "QhgevIUBSWe37q1MP+M/vtktjOcrE74BVbpcxlLQw58=",
+            "6YS6w5wqkpdfkEW7iOP1NvituehFlFRfPko2n7KY4Gk=",
+        )
+        .status(Status::Enabled)
+        .execute()
+        .await?;
+
+    println!("Successfully created a new device '{}'", device.device_id);
+
+    println!(
+        "Setting status to disabled and set IoT Edge capability of device '{}'",
+        device.device_id
+    );
+    let device = service_client
+        .update_device_identity(device.etag)
+        .device_id(device.device_id)
+        .device_capability(DesiredCapability::IotEdge)
+        .authentication_using_sas(
+            "QhgevIUBSWe37q1MP+M/vtktjOcrE74BVbpcxlLQw58=",
+            "6YS6w5wqkpdfkEW7iOP1NvituehFlFRfPko2n7KY4Gk=",
+        )
+        .status(Status::Disabled)
+        .execute()
+        .await?;
+
+    println!("Getting device identity of '{}'", device.device_id);
+    let device = service_client.get_device_identity(device.device_id).await?;
+    println!("Identity is: {:?}", device);
+
+    println!("Deleting device '{}'", device.device_id);
+    service_client
+        .delete_device_identity(device.device_id, None)
+        .await?;
+
+    Ok(())
+}