samples: rpi_pico2: Add ADC-related samples for rpi_pico2

The Raspberry Pi Pico 2's device is compatible with the existing Pico 1.
The build system requires a `<board>.overlay` file, but these use the
pre-processing to #include the sibling rpi_pico.overlay files rather
than duplicating the contents as an attempt to keep things DRY.

Tested locally.

Signed-off-by: Andrew Featherstone <andrew.featherstone@gmail.com>

Author: ajf58

samples/drivers/adc/adc_dt/boards/rpi_pico2_rp2350a_m33.overlay

@@ -0,0 +1,8 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2024 Andrew Featherstone <andrew.featherstone@gmail.com>
+ */
+
+/* Pico 2 is compatible with the Pico 1, so reuse. */
+#include "rpi_pico.overlay"

samples/sensor/die_temp_polling/boards/rpi_pico2_rp2350a_m33.overlay

@@ -0,0 +1,8 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2024 Andrew Featherstone
+ */
+
+/* Pico 2 is compatible with the Pico 1, so reuse. */
+#include "rpi_pico.overlay"