app: boards: add support for sample application on nRF9160 DK

Added device tree overlay to support a sample application on the nRF9160 DK.
This includes defining an example sensor and a blink LED. Updated sample.yaml
to include nRF9160 DK in the integration platforms for testing purposes.

Closes: #1

Signed-off-by: Natalia Pluta <pluta.natalia.m@gmail.com>

Author: nmpluta

app/boards/nrf9160dk_nrf9160.overlay

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2025 Natalia Pluta
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	example_sensor: example-sensor {
+		compatible = "zephyr,example-sensor";
+		input-gpios = <&gpio0 11 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+	};
+
+	blink_led: blink-led {
+		compatible = "blink-gpio-led";
+		led-gpios = <&gpio0 5 GPIO_ACTIVE_HIGH>; // Green LED 4 on the nRF9160 DK
+		blink-period-ms = <1000>;
+	};
+};

app/sample.yaml

@@ -10,6 +10,7 @@ common:
   integration_platforms:
     - custom_plank
     - nrf54l15dk/nrf54l15/cpuapp
+    - nrf9160dk/nrf9160
 tests:
   app.default: {}
   app.debug: